A&P Lecture 4.1: Function of the Respiratory System

The cells of the body derive the energy they need from the oxidation of carbohydrates, fats, and proteins. As with any type of combustion, this process requires oxygen. Certain vital tissues, such as those of the brain and the heart, cannot survive for long without a continuous supply of oxygen. However, as a result of oxidation in the body tissues, carbon dioxide is produced and must be removed from the cells to prevent the buildup of acid waste products. The respiratory system performs this function by facilitating life-sustaining processes such as oxygen transport, respiration and ventilation, and gas exchange.

Oxygen Transport

Oxygen is supplied to, and carbon dioxide is removed from, cells by way of the circulating blood. Cells are in close contact with capillaries, the thin walls of which permit easy passage or exchange of oxygen and carbon dioxide. Oxygen diffuses from the capillary through the capillary wall to the interstitial fluid. At this point, it diffuses through the membrane of tissue cells, where it is used by mitochondria for cellular respiration. The movement of carbon dioxide occurs by diffusion in the opposite direction—from cell to blood.

Respiration

After these tissue capillary exchanges, blood enters the systemic veins (where it is called venous blood) and travels to the pulmonary circulation. The oxygen concentration in blood within the capillaries of the lungs is lower than in the lungs’ air sacs (alveoli). Because of this concentration gradient, oxygen diffuses from the alveoli to the blood. Carbon dioxide, which has a higher concentration in the blood than in the alveoli, diffuses from the blood into the alveoli. Movement of air in and out of the airways (ventilation) continually replenishes the oxygen and removes the carbon dioxide from the airways and lungs. This whole process of

gas exchange between the atmospheric air and the blood and between the blood and cells of the body is called respiration.

Ventilation

During inspiration, air flows from the environment into the trachea, bronchi, bronchioles, and alveoli. During expiration, alveolar gas travels the same route in reverse. Physical factors that govern air flow in and out of the lungs are collectively referred to as the mechanics of ventilation and include air pressure variances, resistance to air flow, and lung compliance.

Air Pressure Variances

Air flows from a region of higher pressure to a region of lower pressure. During inspiration, movement of the diaphragm and other muscles of respiration enlarges the thoracic cavity and thereby lowers the pressure inside the thorax to a level below that of atmospheric pressure. As a result, air is drawn through the trachea and bronchi into the alveoli. During expiration, the diaphragm relaxes and the lungs recoil, resulting in a decrease in the size of the thoracic cavity. The alveolar pressure then exceeds atmospheric pressure, and air

flows from the lungs into the atmosphere.

Airway Resistance

Resistance is determined chiefly by the radius or size of the airway through which the air is flowing. Any process that changes the bronchial diameter or width affects airway resistance and alters the rate of air flow for a given pressure gradient during respiration. With increased resistance, greater-than-normal respiratory effort is required to achieve normal levels of ventilation.

Compliance

Compliance, or distensibility, is the elasticity and expandability of the lungs and thoracic structures. Compliance allows the lung volume to increase when the difference in pressure between the atmosphere and thoracic cavity (pressure gradient) causes air to flow in. Factors that determine lung compliance are the surface tension of the alveoli (normally low with the presence of surfactant) and the connective tissue (ie, collagen and elastin) of the lungs. Compliance is determined by examining the volume pressure relationship in the lungs and the thorax. Compliance is normal (1.0 L/cm H2O) if the lungs and thorax easily stretch and distend when pressure is applied. High or increased compliance occurs if the lungs have lost their

elasticity and the thorax is overdistended (eg, in emphysema).

Low or decreased compliance occurs if the lungs and thorax are “stiff.” Conditions associated with decreased compliance include morbid obesity, pneumothorax, hemothorax, pleural effusion, pulmonary edema, atelectasis, pulmonary fibrosis, and acute respiratory distress syndrome (ARDS), which are discussed in later chapters in this unit. Measurement of compliance is one method used to assess the progression and improvement in patients with ARDS. Lungs with decreased compliance require greater-thannormal energy expenditure by the patient to achieve normal levels of ventilation. Compliance is usually measured under static conditions.

Lung Volumes and Capacities

Lung function, which reflects the mechanics of ventilation, is viewed in terms of lung volumes and lung capacities. Lung volumes are categorized as tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume. Lung capacity is evaluated in terms of vital capacity, inspiratory capacity, functional residual capacity, and total lung capacity.

A&P Lecture 1.11: Centrioles and Spindle Fibers

This is an in depth  explanation of Centriloes and Spindle fiber as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.11

CENTRIOLES AND SPINDLE FIBERS

Centrioles and Spindle Fibers

The centrosome, a specialized zone of cytoplasm close to the nucleus, is the center of microtubule formation. It contains two centrioles . Each centriole is a small, cylindrical organelle about 0.3–0.5 μm in length and 0.15 μm in diameter, and the two centrioles are normally oriented perpendicular to each other within the centrosome. The wall of the centriole is composed of nine evenly spaced, longitudinally oriented, parallel units, or triplets. Each unit consists of three parallel microtubules joined together.

Microtubules appear to influence the distribution of actin and intermediate filaments. Through its control of microtubule formation, the centrosome is closely involved in determining cell shape and movement. The microtubules extending from the centrosomes are very dynamic—constantly growing and shrinking. Before cell division, the two centrioles double in number, the centrosome divides into two, and one centrosome, containing two centrioles, moves to each end of the cell.

Microtubules called
spindle fibers extend out in all directions from the centrosome. These microtubules grow and shrink even more rapidly than those of nondividing cells. If the extended end of a spindle fiber comes in contact with a kinetochore, a specialized region in the centromere of each chromosome, the spindle fiber attaches to the kinetochore and stops growing or shrinking. Eventually, spindle fibers from each centrosome bind to the kinetochores of all the chromosomes. During cell division, the microtubules facilitate the movement of chromosomes toward the two centrosomes

A&P Lecture 1.12: Cilia Flagella and Microvilli

This is an in depth  explanation of Lysosomes as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.12

CILLIA, FLAGELLA AND MICROVILLI

Cilia and Flagella

Cilia  are structures that project from the surface of cells and are capable of movement. They vary in number from one to thousands per cell. Cilia are cylindrical in shape, about 10 μm in length and 0.2 μm in diameter, and the shaft of each cilium is enclosed by the plasma membrane. Two centrally located microtubules and nine peripheral pairs of fused microtubules, the so-called 9 2 arrangement, extend from the base to the tip of each cilium. Movement of the microtubules past each other, a process that requires energy from ATP, is responsible for movement of the cilia. Dynein arms, proteins connecting adjacent pairs of microtubules, push the microtubules past each other. A basal body (a modified centriole) is located in the cytoplasm at the base of the cilium. Cilia are numerous on surface cells that line the respiratory tract and the female reproductive tract. In these regions, cilia move in a coordinated fashion, with a power stroke in one direction and a recovery stroke in the opposite direction. Their motion moves materials over the surface of the cells. For example, cilia in the trachea move mucus embedded with dust particles upward and away from the lungs. This action helps keep the lungs clear of debris.

Flagella  have a structure similar to cilia but are longer (45 μm). Sperm cells are the only human cells to possess flagella and usually only one flagellum exists per cell. Furthermore, whereas cilia move small particles across the cell surface, flagella move the entire cell. For example, each sperm cell is propelled by a single flagellum. In contrast to cilia, which have a power stroke and a recovery stroke, flagella move in a

wavelike fashion.

Microvilli

Microvilli ) are cylindrically shaped

extensions of the plasma membrane about 0.5–1.0 μm in length and 90 nm in diameter. Normally, many microvilli are on each cell, and they function to increase the cell surface area. A student looking at photographs may confuse microvilli with cilia. Microvilli, however, are only one-tenth to one-twentieth the size of cilia. Individual microvilli can usually be seen only with an electron microscope, whereas cilia can be seen with a light microscope. Microvilli do not move, and they are supported with actin filaments, not microtubules. Microvilli are found in the intestine, kidney, and other areas in which absorption is an important

function. In certain locations of the body, microvilli are highly modified to function as sensory receptors. For example, elongated microvilli in hair cells of the inner ear respond to sound.

A&P Lecture 1.10: Mitochondria

This is an in depth  explanation of Mitochondria as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.10

MITOCHONDRIA

All cells in the body, with the exception of mature red blood cells, have from a hundred to a few thousand organelles called mitochondria (singular, mitochondrion ). Mitochondria serve as sites for the production of most of the energy of cells

Mitochondria vary in size and shape, but all have the same basic structure.. Each mitochondrion is surrounded by an inner and outer membrane, separated by a narrow intermembranous space. The outer mitochondrial membrane is smooth, but the inner membrane is characterized by many folds, called cristae, which project like shelves into the central area (or matrix ) of the mitochondrion. The cristae and the matrix compartmentalize the space within the mitochondrion and have different roles in the generation of cellular energy.

Mitochondria can migrate through the cytoplasm of a cell and are able to reproduce themselves. Indeed, mitochondria contain their own DNA. All of the mitochondria in a person’s body are derived from those inherited from the mother’s fertilized egg cell. Thus, all of a person’s mitochondrial genes are inherited from the mother. Mitochondrial DNA is more primitive (consisting of a circular, relatively small, doublestranded

molecule) than that found within the cell nucleus. For this and other reasons, many scientists believe that mitochondria evolved from separate organisms, related to bacteria, that invaded the ancestors of animal cells and remained in a state of symbiosis. This symbiosis might not always benefit the host; for example, mitochondria produce superoxide radicals that can provoke an oxidative stress and some scientists believe that accumulations of mutations in mitochondrial DNA may contribute to aging. Mutations in mitochondrial DNA occur at a rate at least ten times faster than in nuclear DNA (probably due to the superoxide radicals),

and there are more than 150 mutations of mitochondrial DNA presently known to contribute to different human diseases. However, genes in nuclear DNA code for 99% of mitochondrial proteins (mitochondrial DNA contains only 37 genes), and so many mitochondrial diseases are produced by mutations in nuclear DNA.

Neurons obtain energy solely from aerobic cell respiration, which occurs in mitochondria. Thus, mitochondrial fission (division) and transport over long distances is particularly important in neurons, where axons can be up to l meter in length. Mitochondria can also fuse together, which may help to repair those damaged by “reactive oxygen species” generated within mitochondria.

A&P Lecture 1.9: Peroxisomes and Proteasomes

This is an in depth  explanation of Peroxisomes and Proteasomes as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.9

PEROXISOMES AND PROTEASOMES

Peroxisomes are membrane-enclosed organelles containing several specific enzymes that promote oxidative reactions. Although peroxisomes are present in most cells, they are particularly large and active in the liver.

All peroxisomes contain one or more enzymes that promote reactions in which hydrogen is removed from particular organic molecules and transferred to molecular oxygen (O 2 ), thereby oxidizing the molecule and forming hydrogen peroxide (H 2 O 2 ) in the process. The oxidation of toxic molecules by peroxisomes in this way is an important function of liver and kidney cells. For example, much of the alcohol ingested in alcoholic drinks is oxidized into acetaldehyde by liver peroxisomes.

The enzyme catalase within the peroxisomes prevents the excessive accumulation of hydrogen peroxide by catalyzing

Proteasomes  consist of large protein complexes, including several enzymes that break down and recycle proteins within the cell. Proteasomes are not surrounded by membranes. They are tunnel-like structures, similar to channel protein complexes; the inner surfaces of the tunnel have enzymatic regions that break down
proteins. Smaller protein subunits close the ends of the tunnel and regulate which proteins are taken into it for digestion.the reaction 2H 2 O 2 → 2 H 2 O + O 2 . Catalase is one of the fastest acting enzymes known (see chapter 4), and it is this reaction that produces the characteristic fizzing when hydrogen peroxide
is poured on a wound.

A&P Lecture 1.8: Lysosomes

This is an in depth  explanation of Lysosomes as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.8

LYSOSOMES

After a phagocytic cell has engulfed the proteins, polysaccharides, and lipids present in a particle of “food” (such as a bacterium), these molecules are still kept isolated from the cytoplasm by the membranes surrounding the food vacuole. The large molecules of proteins, polysaccharides, and lipids must first be digested into their smaller subunits (including amino acids, monosaccharides, and fatty acids) before they can cross the vacuole membrane and enter the cytoplasm.

 The digestive enzymes of a cell are isolated from the cytoplasm and concentrated within membrane-bound organelles called lysosomes, which contain more than 60 different enzymes. A primary lysosome is one that contains only digestive enzymes (about 40 different types) within an environment that is more acidic than the surrounding cytoplasm. A primary lysosome may fuse with a food vacuole (or with another cellular organelle) to form a secondary lysosome in which worn-out organelles and the products of phagocytosis can be digested. Thus, a secondary lysosome contains partially digested remnants of other organelles and ingested organic material. A lysosome that contains undigested wastes is called a residual body. Residual bodies may eliminate their waste by exocytosis, or the wastes may accumulate within the cell as the cell ages.

Partly digested membranes of various organelles and other cellular debris are often observed within secondary lysosomes. This is a result of autophagy, a process that destroys worn-out organelles and proteins in the cytoplasm so that they can be continuously replaced. Lysosomes are thus aptly characterized as the “digestive system” of the cell.

Lysosomes have also been called “suicide bags” because a break in their membranes would release their digestive enzymes and thus destroy the cell. This happens normally in programmed cell death (or apoptosis ), . An example is the loss of tissues that must accompany embryonic development, when earlier structures (such as gill pouches) are remodeled or replaced as the embryo matures

SUMMARY

Lysosomes  are membrane-bound vesicles that pinch off from the Golgi apparatus. They contain a variety of hydrolytic enzymes that function as intracellular digestion systems. Vesicles taken into the cell fuse with the lysosomes to form one vesicle and to expose the endocytized materials to hydrolytic enzymes. Various enzymes within lysosomes digest nucleic acids, proteins, polysaccharides, and lipids. Certain white blood cells have large numbers of lysosomes that contain enzymes to digest phagocytized bacteria. Lysosomes also

digest the organelles of the cell that are no longer functional in a process called autophagia . In other

cells, the lysosomes move to the plasma membrane, and the enzymes are secreted by exocytosis. For example, the normal process of bone remodeling involves the breakdown of bone tissue by specialized bone cells. Enzymes responsible for that degradation are released into the extracellular fluid from lysosomes produced by those cells.

A&P Lecture 1.7: Secretory Vesicles

This is an in depth  explanation of the Secretory Vesicle as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.7

SECRETORY VESICLE

The membrane-bound secretory vesicles that pinch off from the Golgi apparatus move to the surface of the cell, their membranes fuse with the plasma membrane, and the contents of the vesicle are released to the exterior by exocytosis. The membranes of the vesicles are then incorporated into the plasma membrane.

Secretory vesicles accumulate in some cells, but their contents frequently are not released to the exterior until the cell receives a signal. For example, secretory vesicles that contain the hormone insulin do not release it until the concentration of glucose in the blood increases and acts as a signal for the secretion of insulin from the cells.

A&P Lecture 1.6: Golgi Complex

This is an in depth  explanation of the Golgi Complex as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.4

GOLGI COMPLEX

The Golgi complex, also called the Golgi apparatus, consists of a stack of several flattened sacs . This is something like a stack of pancakes, but the Golgi sac “pancakes” are hollow, with cavities called cisternae within each sac. One side of the stack faces the endoplasmic reticulum and serves as a site of entry for vesicles from the endoplasmic reticulum that contain cellular products. The other side of the stack faces the plasma membrane, and the cellular products somehow get transferred to that side. This may be because the products are passed from one sac to the next, probably in vesicles, until reaching the sac facing the plasma membrane. Alternatively, the sac that receives the products from the endoplasmic reticulum may move through the stack until reaching the other side. By whichever mechanism the cell product is moved through the Golgi complex, it becomes chemically modified and then, in the sac facing the plasma membrane, is packaged into vesicles that bud off the sac. Depending on the nature of the cell product, the vesicles that leave the Golgi complex may become lysosomes, or secretory vesicles (in which the product is released from the cell by exocytosis), or may serve other functions.

The reverse of exocytosis is endocytosis, as previously described; the membranous vesicle formed by that process is an endosome. . This reverse pathway is called retrograde transport, because proteins within the extracellular fluid are brought into the cell and then taken to the Golgi apparatus and the endoplasmic reticulum. Some toxins, such as the cholera toxin, and proteins from viruses (including components of HIV) rely on retrograde transport for their ability to infect cells.

A&P Lecture 1.5: Endoplasmic Reticulum

This is an in depth  explanation of the Endoplasmic Reticulum as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.4

ENDOPLASMIC RETICULUM

The endoplasmic reticulum is a continuous a series of membranes distributed throughout the cytoplasm of

the cell located at the he outer membrane of the nuclear envelope. It is consists of broad, flattened, interconnecting sacs and tubules. The interior spaces of those sacs and tubules are called cisternae and are

isolated from the rest of the cytoplasm.

Most cells contain a system of membranes known as the endoplasmic reticulum, or ER. The ER may be either of two types: (1) a granular, or rough, endoplasmic reticulum or (2) an agranular, or smooth, endoplasmic reticulum. A granular endoplasmic reticulum bears ribosomes on its surface, whereas an agranular endoplasmic reticulum does not. The agranular endoplasmic reticulum serves a variety

of purposes in different cells; it provides a site for enzyme reactions in steroid hormone production and inactivation, for example, and a site for the storage of Ca 2 + in striated muscle cells. The granular endoplasmic reticulum is abundant in cells that are active in protein synthesis and secretion, such as

those of many exocrine and endocrine glands.

The rough endoplasmic reticulum is called “rough” because it has ribosomes attached to it. The ribosomes of the rough endoplasmic reticulum are sites where proteins are produced and modified for secretion and for internal use. The amount and configuration of the endoplasmic reticulum within the cytoplasm depend on the cell type and function. Cells with abundant rough endoplasmic reticulum synthesize large amounts of protein that are secreted for use outside the cell.

Smooth endoplasmic reticulum, which is endoplasmic reticulum without attached ribosomes, manufactures lipids, such as phospholipids, cholesterol, steroid hormones, and carbohydrates. Many phospholipids produced in the smooth endoplasmic reticulum help form vesicles within the cell and contribute to the plasma membrane. Cells that synthesize large amounts of lipid contain dense accumulations of smooth endoplasmic reticulum. Enzymes required for lipid synthesis are associated with the membranes of the smooth endoplasmic reticulum. Smooth endoplasmic reticulum also participates in the detoxification processes by which enzymes act on chemicals and drugs to change their structure and reduce their toxicity. The smooth endoplasmic reticulum of skeletal muscle stores calcium ions that function in muscle contraction.

A&P Lecture 1.1: Cell Membrane

This lecture note on Anatomy and Physiology is linked to A&P Lecture 1: The Cell to further explain the physiology of the Cell Membrane. 

ANATOMY AND PHYSIOLOGY LECTURE NOTE 1.1

CELL MEMBRANE

The outermost component of the cell is the plasma membrane. It is a boundary that separates the substances inside the cell, which are intracellular , from substances outside the cell, which are extracellular.It determines what moves into and out of cells. As a result, the intracellular contents of cells is different from the extracellular environment. The membrane encloses and supports the cell contents. It attaches cells to the extracellular environment or to other cells. The cells’ ability to recognize and communicate with each other takes place through the plasma membrane.

The regulation of ion movement by cells results in a charge difference across the plasma membrane called the membrane potential. The outside of the plasma membrane is positively charged, compared with the inside, because there are more positively charged ions immediately on the outside of the plasma membrane and more negatively charged ions and proteins inside. This concept is paramount in understanding the Sodium Potassium Pump that controls the electrophysiology of the heart, transmission of nerve impulses and contraction of muscles.

The plasma membrane consists of 45%–50% lipids, 45%– 50% proteins, and 4%–8% carbohydrates ( figure 3.2 ). The carbohydrates combine with lipids to form glycolipids and with proteins to form glycoproteins. The glycocalyx (glı¯-ko¯-ka¯ liks) is the collection of glycolipids, glycoproteins, and carbohydrates on the outer surface of the plasma membrane. The glycocalyx also contains molecules absorbed from the extracellular environment, so there is often no precise boundary where the plasma membrane ends and the extracellular environment begins.

Indepth Medical Physiology

The membrane that surrounds cells is a notable structure. It is made up of lipids and proteins and is semipermeable meaning- it allows some substances to pass through it and excluding others. However, its permeability can also be varied because it contains numerous regulated ion channels and other transport proteins that can change the amounts of substances moving across it. It is generally referred to as the plasma membrane. The nucleus and other organelles in the cell are bound by similar membranous structures.

Although the chemical structures of membranes and their properties vary considerably from one location to another, they have certain common features. They are generally about 7.5 nm thick. The major lipids are phospholipids such as phosphatidylcholine, phosphotidylserine, and phosphatidylethanolamine. The shape of the phospholipid molecule reflects its solubility properties: the “head” end of the molecule contains the phosphate portion and is relatively soluble in water  and the “tail” ends are relatively insoluble. The possession of both hydrophilic and hydrophobic properties makes the lipid an amphipathic molecule. In the membrane, the hydrophilic ends of the molecules are exposed to the aqueous environment that bathes the exterior of the cells and the aqueous cytoplasm; the hydrophobic ends meet in the water-poor interior of the membrane. In prokaryotes, the membranes are relatively simple, but in eukaryotes, cell membranes contain various glycosphingolipids, sphingomyelin, and cholesterol in addition to phospholipids and phosphatidylcholine.

Many different proteins are embedded in the membrane. They exist as separate globular units and many pass through or are embedded in one leaflet of the membrane- integral proteins, whereas others- peripheral proteins, are associated with the inside or outside of the membrane. The amount of protein varies significantly with the function of the membrane but makes up on average 50% of the mass of the membrane; that is, there is about one protein molecule per 50 of the much smaller phospholipid molecules.

The proteins in the membrane carry out many functions. Some are cell adhesion molecules that anchor cells to their neighbors or to basal laminas. Some proteins function as pumps, actively transporting ions across the membrane. Other proteins function as carriers, transporting substances down electrochemical gradients by facilitated diffusion. Still others are ion channels, which, when activated, permit the passage of ions into or out of the cell. The role of the pumps, carriers, and ion channels in transport across the cell membrane is discussed below. Proteins in another group function as receptors that bind ligands or messenger molecules, initiating physiologic changes inside the cell. Proteins also function as enzymes, catalyzing reactions at the surfaces of the membrane. 

The uncharged, hydrophobic portions of the proteins are usually located in the interior of the membrane, whereas the charged, hydrophilic portions are located on the surfaces. Peripheral proteins are attached to the surfaces of the membrane in various ways. One common way is attachment to glycosylated forms of phosphatidylinositol. Proteins held by these glycosylphosphatidylinositol (GPI) anchors include enzymes such as alkaline phosphatase, various antigens, a number of CAMs, and three proteins that combat cell lysis by complement. Over 45 GPI-linked cell surface proteins have now been described in humans. Other proteins are lipidated, that is, they have specific lipids attached to them. Proteins may be myristoylated, palmitoylated, or prenylated (ie, attached to geranylgeranyl or farnesyl groups).

The protein structure—and particularly the enzyme content—of biologic membranes varies not only from cell to cell, but also within the same cell. For example, some of the enzymes embedded in cell membranes are different from those in mitochondrial membranes. In epithelial cells, the enzymes in the cell membrane on the mucosal surface differ from those in the cell membrane on the basal and lateral margins of the cells; that is, the cells are polarized. Such polarization makes directional transport across epithelia possible. Th e membranes are dynamic structures, and their constituents are being constantly renewed at different rates. Some proteins are anchored to the cytoskeleton, but others move laterally in the membrane.

Underlying most cells is a thin, “fuzzy” layer plus some fibrils that collectively make up the basement membrane or, more properly, the basal lamina. Th e basal lamina and, more generally, the extracellular matrix are made up of many proteins that hold cells together, regulate their development, and determine their growth. These include collagens, laminins, fibronectin, tenascin, and various proteoglycans.

A&P Lecture 1: The Cell

"You need to know the normal before you can determine the abnormal." 

Knowledge in Anatomy and Physiology is paramount before tackling advance Nursing Courses. It is the reason why Anatomy and Physiology class is taken first before professional courses like Pathophysiology, Medical Surgical Nursing, Maternal and Child Nursing and Psychiatric Nursing.Anatomy and Physiology is a good foundation when you already try to study illnesses. This A&P Lecture Series is designed to help students develop a solid understanding of the concepts of anatomy and physiology and to use this knowledge to solve problems.

ANATOMY AND PHYSIOLOGY LECTURE 1

THE CELL

The Cell is the basic unit of life. Cells are the smallest parts of an organism, such as a human, that have the characteristics of life. Although cells may have quite different structures and functions, they share several characteristics which includes:

• Cell metabolism and energy use
• Synthesis of molecules
• Communication
• Reproduction and inheritance

Plasma Membrane

Structure: Lipid bilayer composed of phospholipids and cholesterol with proteins that extend across or are embedded in either surface of the lipid bilayer

Function: Outer boundary of cells that controls entry and exit of substances; receptor molecules function in intercellular communication; marker molecules enable cells to recognize one another.

***Read more about the Plasma Membrane here

Cytoplasm

Fluid Part

Structure: Water with dissolved ions and molecules; colloid with suspended proteins

Function:Contains enzymes that catalyze decomposition and synthesis reactions; ATP is produced in glycolysis reactions

Cytoskeleton/ Microtubules

Structure: Hollow cylinders composed of the protein tubulin; 25 nm in diameter

Function: Support the cytoplasm and form centrioles, spindle fibers, cilia, and flagella; responsible for movement of structures in the cell

Actin Filaments

Structure: Small fibrils of the protein actin; 8 nm in diameter

Function: Provide structural support to cells, support microvilli, responsible for cell movements

Intermediate Filaments

Structure:Protein fibers; 10 nm in diameter

Function: Provide structural support to cells

Cytoplasmic Inclusions

Structure:Aggregates of molecules manufactured or ingested by the cell; may be membrane-bound

Function: Function depends on the molecules: energy storage (lipids, glycogen), oxygen transport (hemoglobin), skin color (melanin), and others

*** Read More about the Cytosol and its components here

Organelles, Nucleus

Nuclear envelope

Structure:Double membrane enclosing the nucleus; the outer membrane is continuous with the endoplasmic reticulum; nuclear pores extend through the nuclear envelope

Function: Separates nucleus from cytoplasm and regulates movement

of materials into and out of the nucleus

Chromatin

Structure:Dispersed, thin strands of DNA, histones, and other proteins; condenses to form chromosomes during cell division

Function: DNA regulates protein (e.g., enzyme) synthesis and therefore the chemical reactions of the cell; DNA is the genetic, or hereditary, material

Nucleolus

Structure: One or more dense bodies consisting of ribosomal RNA and proteins

Function: Assembly site of large and small ribosomal subunits

***Read more about the Nucleus and it's components here

Cytoplasmic Organelles

Ribosome

Structure:Ribosomal RNA and proteins form large and small subunits; attached to endoplasmic reticulum or free ribosomes are distributed throughout the cytoplasm

Function: Site of protein synthesis
 ***Read more about Ribosome here

Rough endoplasmic reticulum

Structure: Membranous tubules and flattened sacs with attached ribosomes

Function: Protein synthesis and transport to Golgi apparatus

*** Read more about the Endoplasmic Reticulum here

Smooth endoplasmic reticulum

Structure: Membranous tubules and flattened sacs with no attached ribosomes

Function: Manufactures lipids and carbohydrates; detoxifies harmful chemicals; stores calcium
*** Read more about the Endoplasmic Reticulum here

Golgi apparatus

Structure: Flattened membrane sacs stacked on each other

Function: Modifies, packages, and distributes proteins and lipids for secretion or internal use

***Read more about the Golgi apparatus here

Secretory vesicle

Structure: Membrane-bound sac pinched off Golgi apparatus

Function: Carries proteins and lipids to cell surface for secretion

***Read more about the Secretory vesicle here

Lysosome

Structure: Membrane-bound vesicle pinched off Golgi apparatus

Function: Contains digestive enzymes
***Read more about the Lysosomes  here

Peroxisome

Structure: Membrane-bound vesicle

Function: One site of lipid and amino acid degradation; breaks down hydrogen peroxide

***Read more about Peroxisome here

Proteasomes

Structure: Tubelike protein complexes in the cytoplasm

Function: Break down proteins in the cytoplasm
***Read more about Proteasomes here

Mitochondria

Structure: Spherical, rod-shaped, or threadlike structures; enclosed by double membrane; inner membrane forms projections called cristae

Function: Major site of ATP synthesis when oxygen is available
***Read more about the Mitochondria here

Centrioles

Structure: Pair of cylindrical organelles in the centrosome, consisting of triplets of parallel microtubules 

Function: Centers for microtubule formation; determine cell polarity during cell division; form the basal bodies of cilia and flagella

***Read more about the Centriole here

Spindle fibers

Structure:Microtubules extending from the centrosome to chromosomes and other parts of the cell (i.e., aster fibers)

Function: Assist in the separation of chromosomes during cell division

***Read more about the Spindle fiber here

Cilia

Structure: Extensions of the plasma membrane containing doublets of parallel microtubules; 10 μm in length

Function: Move materials over the surface of cells
***Read more about the Cilia here

Flagellum

Structure: Extension of the plasma membrane containing doublets of parallel microtubules; 55 μm in length

Function: In humans, responsible for movement of spermatozoa

***Read more about the Flagellum here

Microvilli

Structure: Extension of the plasma membrane containing microfilaments

Function: Increase surface area of the plasma membrane for absorption and secretion; modified to form sensory receptors

***Read more about the Microvillli here