Princeton Review Ch 10 - Excretory and Digestive System Flashcards
Summary of liver function.
The liver is responsible for excreting many wastes by chemically modifying them and releasing them into bile. Liver deals with hydrophobic or large waste products that cannot be filtered by the kidneys (kidney only rids of small hydrophilic products). Ex. Heme broken down into bilirubin. Liver also synthesizes urea.
Colon - summary of function.
Reabrosb water and ions (sodium, Ca, etc) from feces. Colon can also release excess ions (Na, Cl-, Ca)
Skin - summary of function in terms of excretion.
Skin produces sweat, which contains water, ions and urea.
Summary of excretory and homeostatic roles of the kidney
1) Excretion of hydrophilic waste.
2) Maintenence of constant solute concentration and constant pH.
3) Maintainence eof constant fluid volume (important for blood pressure and cardiac output.
Broadly, explain the four steps to urine production.
1) Filtration - passing pressurized blood over a filter, while water and small molecultes are squeezed into the renal tubule
2) selective reabsorption of useful items like glucose, water, and amino acids
3) secretion - addition of substances to filtrate
4) Concentration and dilution - selective reabsorption of water and where we decided whether to make it dilute or concentrated.
Renal capsule, tubule, and collecting duct.
A round region surrounding the capillaries where filtration takes place is known as the renal capsule and the renal tubule. The renal tubule receives filtrate from the capillaries in the capsule at one end and empties into a collecting duct on the other. The collecting duct dumps urine into the renal pelvis.
Blood enters kidneys from the ____.
Renal artery, which is a direct branch of the lower portion of the aorta (abdominal aorta). Purfied blood is returned from the renal vein.
1) Filtration - afferent arteriole, glomerulus, efferent arteriole, glomerular basement, and Bowman’s capsule.
Blood from the renal artery flows into the afferent arteriole, which brancesh into a ball of capillaries called the glomerulus. From there blood flows into an efferent arteriole. Constriction of this results in high BP in the glomerulus, which causes fluid to pass through the glokerular basement membrane filter and enters the Bowman’s capsule.
2) Selective reabsorption.
Many substances, like glucose are extracted from the tubule, often via active transportion and picked up by peritibular capillaries. The tubule nearest to the Bowman’s capsule, called the proximal convoluted tubule is the area with the greater amount of reabsorption.
Where can reabsorption take place in a nephron. Which is more regulated.
Most reabsprtion of substances and water (about 70%) takes place in the proximal tubule. All solute movement is accompanied by water in many of the cases in the PCT. Selective reabsorption also takes place in the distal convoluted tubule, but this location is more regulated, particulary by hormones.
True or false. 100% of glucose is normally reclaimed during urine production.
True. Unless you’re diabetic. Glucose reabsoprtoion is difficult when the cotransporters responsible are saturated.
Where does secretion typially happen in a nephron?
The distal convoluted tubule or collecting duct. This is a back up method to ensure what needs to be eliminated, gets elimnated.
Function of ADH/vasopressin.
Antidirectic hormone is released by the posterior pituitary. This prevents diuresis (loss of water in urine) by increase water reabsorption in the distal nephron (distal convoluted tubule or collecting duct). This is done by making that region permeable to water. Because of the high osmolarity of blood, water will flow out of filtrate and into the kidney tissues and then peritubular capillaries. When you’re dehydrated, the volume of fuild in the bloodstream is low and the solute [ ] is high.
Function of aldosterone
When BP is low, aldosterone is released by the adrenal cortex. It causes an increase in reabsorption of Na+ by the distal nephron. The result is increased plasma osmolarity, which leads to thirst and water retention, which raises the BP.
Angiotensin 2.
Triggers release of aldosterone, which serves to increase osmolarity and thus blood pressure.
How does ADH and aldosterone work together?
ADH and aldoesterone work together to increase blood pressure. First aldoesterone causes Na reabsorption, which results in increase plasma osmolarity. This causes ADH to be secreted, which results in increased water reabsorption and thus increased plasma volume.
The loop of henle is a _____ that makes the ___ very salty, and this facilitates ____ reabsorption from the collecting duct (in the presence of ADH). This is how the kidney is capable of making urine with a much higher osmolarity than plasma.
The loop of henle is a countercurrent multiplier that makes the renal medulla very salty, and this facilitates water reabsorption from the collecting duct (in the presence of ADH). This is how the kidney is capable of making urine with a much higher osmolarity than plasma.
Vasa recta and countercurrent exchange.
The vasa recta form a loop that helps to maintain the high concentration of salt in the medulla. The ascending portions of the vasa recta are near the descending portion of the LOH and thus carries water that leaves the descending limb. Becaues the blood in the vasa recta moves in the opp direction of hte filtrate, the vasa recta performs countercurrent exchange.
Juxtaglomerular appratus components and function.
The JGA is a special contact point between the afferent arteriole and the distal tubule. At this contact point, the cells in the afferent arterial are called juxtaglomerular cells, and those in the distal tubule is called the macula densa. These two components help manage blood pressure, since the glomerular filtration rate depends on pressure.
Juxtraglomerular cell and macula cell function.
JG cells are baroreceptors that monitor systemic BP. Where there is a decrease in BP, the cells secrete and an enzyme called renin, which catalyzes the conversion of angiotensin into angiotensin I, which is converted to angiotensin II by angiotensin-converting enzyme (ACE) in the lungs. AGII is a powerful vasoconstrictor and also stimulates the release of aldosterone, which increase Na retention and thus water. The cells of the macula densa are chemoreceptors that monitor filtrate in the distal tubule and stimulates the JG to release renin.
How doe the kidneys regulate pH?
When plasma pH is too high, HCO3- is excreted in the urine; when pH is too low, H+ is excreted. This is accomplished via the help of carbonic anhydrase, which catalyzes the conversion of CO2 to H2CO3.
The lungs can regulate pH as well. How?
By exhaling CO2, the lungs remove an acid (H2CO3) from the blood and thus raising pH.
Where calcitonin is produce and its function.
Calcitonin is produced by C cells located in the thyroid gland. Calcitonin is secreted when [Ca2+] is too high. It causes Ca to be removed from blood by: 1) deposition in the bone, 2) reduced absorption by the gut, 3) excretion in the urine.
Where is parathyroid hormone produced and what does it do?
Parathyroid hormone are produced from the four parathyroid glands, found embedded in the thyroid gland. The function of the parathormone (PTH) is the opposite that of the calcitonin.
Where is erythropoietin produced and why is it important.
EPO cause increased synthesis of RBCs in the bone marrow. It is released when blood oxygen content falls.
Catabolic versus anabolic reactions.
Catabolic - reactions that break down molecules to supply energy
Anabolic - the synthesis of macromolecules
3 functions of the digestive system:
DIgestion (breakdown of polymers into their building blocks), absorption, and protection from disease.
How is digestion accomplished?
Enzymatic hydrolysis. So water is used.
Describe the GI epithelium in terms of apical surfaces, basement membranes, microvilli, and tight junctions.
The surface of the epithelial cells that faces the lumen is the apical surface, and in the small intestine, the apical surface contains microvilli to increase SA. The epithelial cells are attached to the basement membrane The apical surface is separated by the remainder of the cell by tight junctions, which are bands running all the way around the sides of the epithelial cells, which separates body fluid from the extracellular environment.
What kind of muscle is in the GI tract?
Circular and longitudinal smooth muscle. Striated = skeletal and cardiac.
Describe movement of a bolus in the GI tract.
Movement is accomplished by an orderly form of contraction called peristalsis. Contraction of smooth muscle at point A prevents food located at point B from moving backward. Contraction of longitudinal muscle at point B results in shortening the gut, and moving the food forward.
How is GI smooth muscle and cardiac muscle similar?
1) Automaticity. It contracts periodically without external stimulation, due to spontaneous depolarization.
2) Like cardiac muscle, GI smooth muscle is a functional syncytium, meaning when one cell has an AP and contracts, the impulse spreads to neighboring cells.
True or false. The GI contains its own nervous system.
True. It’s called the enteric nervous system, and it is a branch of the autonominc nervous system.
Mesenteric plexus versus submucosal plexus.
1) The mesenteric plexus is found between circular and longitudinal muscle layer and helps primarily to regulate gut motility.
2) The submucosal plexus is found in the submucosa and helps to regulate enzyme secretion, gut blood flow, and ion/water balance in the lumen
Endocrine versus exocrine.
Exocrine glands are composed of specialized epithelial cells, organized into sacs called acini. Acinar cells secrete products which pass into ducts. Endocrine secretions do not empty into ducts but are instead picked up by nearby capillaries.
Globlet cells.
Mucus-secreting cells in the digestive tract. An exocrine gland.
Organs of the GI tract involved with exocrine secretions.
Pancrease, gallbladder, and liver. However, there are also mini exocrine glands: gastric glands of the stomach and mucus-secreting globet cells.
The function of mucous membranes.
Protects and lubricates the digestive tract.
The mouth has three roles of digestion of food:
1) fragmentation
2) lubrication
3) some enzymatic digestion (sugar and fat) but not protein
Mastication, incisors, cuspids, and molars.
Mastication: chewing
Inscosors: for cutting
cuspids: canine teeth for tearing
molars: for grinding
