Structure and Function of the Human Body week 8

Atmospheric air takes a specific pathway from the external environment to our internal lungs. Describe this pathway starting with external nares to the alveoli. What role does the trachea and surfactant play within the respiratory system?
1. Gas exchange within the lungs and body tissues is vital for life to exist. Briefly explain the gas exchange that occurs in the lung tissue and the body tissue for oxygen and carbon dioxide. What is the driving force for this movement of gas (think concentration gradient)? Finally, how does carbon monoxide disrupt the process of oxygen transport?

1. Air enters the respiratory system through the nostrils (external nares) where the air is being filtrated, warmed, and humidified.
Air is then passed through the pharynx which is also called the throat. It also shares its chamber with the esophagus.
From the throat, it passes through an open glottis allowing the air to enter the larynx (voice box) Within the larynx, you have an elastic mechanism called the epiglottis that protects the trachea from food and liquid entering the respiratory tract.
Air leaving the larynx passes into the trachea. The trachea is a sturdy, flexible tube that does double duty. The trachea protects the airway from over expansion and collapsing due to respiratory pressure changes and it consists of a series of c-shape rings which makes it stable and flexible. Since the esophagus runs parallel posteriorly to the trachea, the open portions of the trachea’s C-shaped rings face posterior toward the esophagus that allows a bending movement of the trachea and easily allows food to pass through the esophagus.
Air from the trachea passes through the larger right and smaller left bronchi that descends into the right and left lungs. In the lungs, the bronchi re-branches into the secondly bronchi that eventually re-branches into tiny bronchioles. Air movement into the tiny bronchioles finally terminates in a cluster of alveoli, where the gases are exchanged. (pp. 504-511)

Surfactant is an important oily substance secreted by septal cells that covers the thin layer of water coating on the alveolar surface. Water provides surface tension; therefore, surfactant main purpose is to decrease surface tension. Surfactant promotes easy expansion (inhale) of the alveoli and prevents the alveoli from collapsing during exhale. It also reduces the effort needed for the lungs to expand and contract during breathing. It is almost like WD40 that is needed to lubricate tools, so it works better and smoother. (pg 511-512)

2. Gas exchange within the lungs and body tissues is vital for life to exist. Briefly explain the gas exchange that occurs in the lung tissue and the body tissue for oxygen and carbon dioxide. What is the driving force for this movement of gas (think concentration gradient)? Finally, how does carbon monoxide disrupt the process of oxygen transport?

2. The primary function of the respiratory system is to obtain oxygen for use by the body’s cells and eliminate carbon dioxide that cells produce. This is done through external and internal respiration. External respiration involves exchange of oxygen and carbon dioxide between the body’s cells and the external environment. External respiration involves pulmonary ventilation, gas diffusion (two sites: across the respiratory membrane, between the alveolar airspace and alveolar capillaries and across the capillary cell membrane between blood and tissue), and finally transportation of oxygen carbon dioxide between the alveolar capillaries and capillary beds of tissues. Internal respiration is the absorption of oxygen and the release of carbon dioxide into the cells. Both external and internal occurs through simple diffusion with partial pressure gradient. (pg 514, 518-521)

The process of gas exchange (O2 and CO2) between the alveoli and the blood occurs by a simple process of diffusion, membrane permeability (respiratory membrane), and pressure. Diffusion requires a concentration gradient ( or pressure). With O2 in the alveoli, pressure (concentration) must be kept at a higher level than in the blood, and pressure (concentration) of CO2 in the alveoli must be kept at a lower level than in the blood. Of course, this whole process occurs through normal breathing. (pg 518-521)

External air (atmospheric) consists mainly of nitrogen (N2), oxygen (O2), water vapor (H2O), and carbon dioxide (CO2). The total atmospheric pressure equals 760 mm Hg. Each gas contributes a partial pressure (P) of the total pressure. For example, PO2 is approximately 20.9% of the total pressure 760 mm Hg. Oxygen is considered a partial pressure (P) of the total. In other words, each gas determines the rate of diffusion between alveolar air and the blood stream. O2 is most affected by diffusion rate whereas CO2 and nitrogen has no effect. (pg 518)

Air entering the alveolar capillaries consists of lower PO2 (40 mm Hg), because systemic circulation, blood consists of spent O2. The PCO2 is 45 mm Hg higher because systemic circulation has picked up carbon dioxide. Diffusion between the alveolar air and the pulmonary capillaries elevates the PO2 to 100 mm Hg in the blood and lowers the PCO2 to 40 mm Hg in the alveolus. This process is called external respiration. Blood then leaves the alveolar capillaries, and returns to the left atrium, to the left ventricle and then travels into the systemic circulation. (pg 518-521)

Internal respiration is the diffusion of gases between blood and interstitial membranes. Diffusion between the systemic capillaries and the interstitial fluid lowers the PO2 of the blood and increases the PCO2. In the cells, diffusion between the systemic capillaries and the interstitial fluid lowers the PO2 to 40 mm Hg and raises the PCO2 to 45mm Hg; therefore, the cells take in most of the oxygen for metabolism and release CO2 (waste), as a byproduct of the cellular aerobic metabolism. (pg 514, 518-521)

Hemoglobin plays an important role in intracellular gas exchange, because the iron ion found in each hem unit binds O2; therefore, the amount of oxygen bound or released by hemoglobin depends primary on the PO2 of its surroundings. In other words, the lower the oxygen tissue content, the more oxygen is released by hemoglobin and visa versa. The pH and temperature also have an influence on the amount of O2 released by hemoglobin. If the pH of the interstitial fluid decreases (increase cellular metabolism), or the body’s temperature rises (with increase body activity), hemoglobin will release more O2 at a given PO2 point. The carbon dioxide also increases or decreases due the cellular metabolism. After the carbon dioxide has generated from the cellular metabolism, it enters the bloodstream and will dissolve in the plasma, or bind with hemoglobin, or convert to carbonic acid. (pg 519-521)

Carbon monoxide (CO) arriving from exhaust of automobiles, fuel-fire space heaters, and other burning fuels can become deadly to the human being. Carbon monoxide does produce a low partial pressure (P) and has a high infinity to hemoglobin; therefore, the bonding of CO makes the heme less available to the O2. If enough hemoglobin is affected, survival is diminished through suffocation. This situation is due to carbon monoxide poisoning. (pg 521)

3. One of the kidney’s main roles is elimination of wastes, where blood is filtered and the wastes are excreted via the urethra. Please describe the pathway a waste product in the blood takes (for example urea) starting with an afferent arteriole to the urethra. Finally, what is the difference between the male and female urethras and what complication could result in females because of this difference?

Creatinine is a by product of muscle metabolism. Creatinine enters the afferent arterioles. It flows into the nephron which begins at the renal corpuscle (glomerular capsule) that contains the capillary network. Filtration of plasma and urine formation starts here. The efferent arteriole departs at this site.

The filtrate solution enters the renal tubule which consists of proximal convoluted tubule (PCT) , nephron loop and distal convoluted tubule (DCT). In the PCT, the reabsorption of ions, organic molecules, vitamins, and water occur. The Nephron loop (descending limb: reabsorbs water from the tubular fluid. The ascending limb of the nephron loop reabsorbs ions, and creates concentration gradient in the medulla, which enables the kidneys to produce concentrated urine. DCT has a hormonal reabsorbtion variant with sodium and water, and also secretes acid, ammonia, drugs and toxin.

From the DCT, the filtrate solution flows into the collecting duct. Here the reabsorption of extra water and sodium and bicarbonate ions occur.

It goes into the papillary duct, which delivers creatinine in the urine to the minor calyx which merges into the major calyces, both combine flows into the renal pelvis. At this point, filtration, modification and urine production ends. Creatinine does not reabsorb.

Urine with creatinine now flows to ureters which eventually flows into the urinary bladder (reservoir of urine). The urine creatinine flows through the urethra and out through the meatus. (pg 618)

The difference between the female and the male urethra is the length of urethra and function. Male urethra is usually 7-8 inches in length. This urethra in males transports both urine and semen and the meatus is located at the tip of the penis. The female urethra is only 1 inch in length, transfers urine only through the urethra and is located between the clitoris and vagina. Women are prone to infection , because of the location of the urethra and the shortness of the urethra. Urinary tract infection are more common in women, because of this. The short length of the urethra can also cause infection that progresses into the bladder (cystitis) and can potentially affect the kidneys (pyelonephritis). (pg 618-619)

4. Urine formation consists of three basic processes; briefly describe each process and the parts of the nephron that are vital to that process. How does glomerular filtration rate correlate to urine formation?

With urine formation, there are three basic processes that take place in different parts of the nephron.

Filtration is one process where it occurs in the renal corpuscle across the glomerular capillary walls. In filtration, blood pressure is the main force needed for water to cross the filtration membrane. Molecular solute that are small enough to pass through the membrane are carried in the filtrate by surrounding water molecules. That is because the glomerular capillaries are said to be fenestrated where the endothelial cells contain pores. The filtration membrane (fenestrated capillaries, basement membrane, and filtration slits) prevents passages of blood cells and most plasma proteins; however, it permits water, mellobolic wastes, and other valuable solutes such as glucose, amino acids. (pg 608-609)

Reabsorption is another basic process where the removal of water and solute molecules from the filtrate is reentered into the circulation at the peritubular capillaries. This occurs mainly at the proximal convulated tubule (PCT). Reabsorption of solutes is the selective process involving simple diffusion (high concentration to low concentration). Water reabsorption occurs passively through osmosis ( passes through semipermeable membrane toward a solution containing a relatively high solute concentration until the solute concentration is equal ).

Secretion is the third basic process. Active secretion occurs primarily at the distal convoluted tubule. Secretion is the transport of solutes from the peritubular capillaries across the tubular epithelium and into the filtrate. Secretion also further lowers plasma concentration of undesirable material that were unable to be filtrated initially such as ions, acids, drugs and toxins. (pg 606-608)

The process of filtration is called glomerular filtration. The amount of filtrate produced in the kidneys in each minute is called is called glomerular filtration rate (GFR). On the average, the glumeruli generate about 180 liters of filtrate urine per day,70 times the total blood plasma; however, 99 % of the filtrate is return when it passes through the renal tubules.

The glomerular correlates with urine formation by two means sympathetic activation and hormonal control.

Autonomic regulation of kidney function occurs through the sympathetic division of the ANS. When activated, the sympathetic essentially shifts blood away from the kidneys which decreases the GFR which does it in a direct means or indirect means. A direct effect constricts the afferent arterioles, decreasing the GFR and slowing the production of filtrate. This can happen during a heart attack where the BP decreases and the sympathetic division promptly overrides the local regularly mechanism. When the crisis passes, the sympathetic division decreases and the GFR capital resumes normal function. The indirect method can derive from strengious activity. The sympathetic division changes the regional pattern of blood circulation which affects the kidneys. Blood flow is increased in the skin and skeletal muscles and less to the kidneys. The danger in this case might be glomerular cells damage , because of low oxygen level and the build up of metabolic wastes. Thankfully, this problem is only temporary for most people and generally can be resolved within 48 hours; however, for a few, it may become permanent impairment. (pg 614- 615)

Hormones have an impact on the kidney GFR also, especially the renin antiotensin system. When the glomerular pressures system, because of a decrease in blood volume, a fall in systemic pressures, or a blockage in the renal artery or its tributaries and juxtaglomerular complex releases the enzyme renin into the circulation. Renin converts inactive angiotensinogen to angiotensin I which a converting enzyme activates to angiotensin II. It has several systems. The peripheral capillary beds causes a brief, but powerful vasoconstriction, elevating blood pressure in the renal arteries. At the nephron, it triggers consentration of the efferent arterioles, evevating glomerular pressures and filtratoin rates. The ADH, which in turn stimulates the reabsorption of water and sodium ion and induces the sensation of thirst. At the suprarenal gland, it stimulates the secretion of aldosterone by the suprarenal cortex and epinephrine of aldosterone by the suprarenal cortex and of espinephrine (E) and norepinephrine (NE) by suprarenal medullae. (pg 615-616)

The antidiuretic hormone increases the water permeability of the DCT and collecting duct, stimulating the reabsorption of water from the tubular fluid and induces the sensation of thirst, leading to the consumption of additional water from the tubular fluid and increases the sensation of thirst, leading to the consumption of additional water.

The aldosterone secretion stimulates the reabsorption of sodium ions and secretion of potassium ions along the DCT and connecting duct. The aldosterone secretion is activated when angiotensin II is stimulated and in response to a rise in the potassium ion concentration of the blood.

The actions of atrial natriurtic peptide (ANP) oppose those of the renin-angiotensin system. The hormone is released by atrial cardiac muscle cells when blood volume and blood pressure are too high. The actions of ANP that affect the kidneys include (1) a decrease in the rate of sodium ion reabsorption in the DCT, leading to increased sodium ion loss in the urine or (2) dilation of glomerular capillaries, which results in increased glomerular filtration and urinary water loss and (3) inactivation of the renin-angiotensin system through the inhibition of rein, aldosterone, and ADH secretion. (pg 617)

The sympathetic division and the hormonal division both have an impact in increasing and decreasing the GFP.

5. The kidneys also play a vital role in maintaining the volume of water and other solutes (like electrolytes) in our blood. How does the urinary system regulate the volume of water within our bodies? How does it regulate sodium?

The kidneys play a vital role in maintaining the volume of water and other solutes like electrolytes by several means. First, it regulates blood volume and blood pressure by adjusting the volume of water lost in the urine, releasing erythropoietin, and releasing renin. Second, regulating plasma concentrations of sodium, potassium, chloride and ions, by controlling the quantities lost in the urine and by controlling the concentration of calcium ions through the synthesis of calcitriol. Third, helping to stabilize blood pH by controlling loss of hydrogen ions (H+) and bicarbonate ions (HCO3-) in the urine. And conserving valuable nutrients such as glucose and amino acids, by preventing their excretion in the urine, while excreting organic waste products. (pg 602)

The sodium balance in the extracellular fluid (ECF) has to do with sodium ion absorption a the digestive tract and sodium excretion at the kidneys and other sites. Sodium losses occur primarily through urinary excretion and perspiration. The kidney has a great role in regulating sodium ion losses. In response to circulating aldosterone, the kidneys reabsorb sodium ions which decrease sodium loss and in response to atrial natriuretic peptide, the kidneys increase the loss of sodium ions. (pg 623)

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