MCAT BIO CH. 10 PART 1 Flashcards
What are the organs of the excretory system?
- Liver
- Colon
- Skin
- Kidneys
What is the liver responsible for?
Excreting many wastes by chemically modifying them and releasing them into bile
What type of products does the liver deal?
Hydrophobic or large waste products that cannot be filtered out by kidney
What can the kidney dissolve?
Eliminate small hydrophils dissolved in plasma
Which organ synthesizes urea?
The liver
Where does the liver excrete urea?
Into the bloodstream
What is urea?
A carrier of excess nitrogen resulting from protein breakdown
Why must free nitrogen be converted into urea?
Because free ammonia is toxic
What is the purpose of the large intestine?
Reabsorb water and ions from feces
What does the skin produce and how is it an excretory organ?
Produces sweat; excretory role is secondary as its used for temperature level
What is the purpose of kidneys?
Excretion of hydrophilic wastes
Which substances must be excreted in the urine?
Urea, sodium, bicarbonate and water
What is the role of the kidney based on its excretion?
Homeostasis
What are the excretory and homeostatic roles of the kidney?
- Excretion of hydrophilic wastes
- Maintenance of constant solute concentration and constant pH
- Maintenance of constant fluid volume
What is the first process of the kidney in keeping homeostasis?
Filtration
What is the filtration of the kidney?
Passage of pressurized mood over a filter
What does the kidney filter?
Cells and proteins remain in the blood; water and small molecules are squeezed out into the renal tubule
What is the fluid in the renal tubule of the filtration kidney called?
Filtrate
What is the second process of the kidney in keeping homeostasis?
Selective reabsorption
What happens during selective reabsorption of kidney homeostasis?
Take back useful items and leave wastes and some water in the tubule
What is the third process of the kidney in keeping homeostasis?
Secretion
What is secretion based on kidney homeostasis?
Involves addition of substances to the filtrate
What is the last step to urine formation?
Concentration and dilution
What is concentration and dilution based on urine formation?
Selective reabsorption of water
How does the blood enter the kidney?
Fro a large renal artery directly backed of the low protein of the abdominal aorta
How is purified blood return into the body from the kidney?
By the large renal vein which empties into the inferior vena cava
Through what does urine live each kidney and what does it empty in?
Urine leaves each kidney in a ureter and empties into the urinary bladder
What happens when the bladder becomes full?
Signals of urgency are sent to the brain
What are the two sphincters controlling the release of urine?
Internal sphincter and external sphincter
What is the internal sphincter based on bladder control, made of?
Made of smooth involuntary muscle
What is the external sphincter based on bladder control, made of?
Made of skeletal voluntary muscle
What is the name of the outside layer of the kidney? What about right underneath these layers?
- Cortex
2. Outer medulla and inner medulla
Why is there striation within the medulla pyramids?
Due to presence of many collecting duct
What are collecting ducts based on the kidney?
Urine empties from the collecting ducts and leaves the medulla at the tip of a pyramid known as a papilla
What does the papilla of the kidney empties?
Calyx
What does the calyx of the kidney converge into?
Renal pelvis
What does the renal pelvis of the kidney empties into?
Ureter
What is the functional unit of the kidney?
The nephron
What are the two components that consist of the nephron?
- Capsule
2. Renal tubule
What is the capsule used as?
Rounded region surrounding the capillaries where filtration takes place
Where does the renal tubule of the kidney receive filtrate from? Where does it empty?
Receives from the capillaries in the capsule and empties into a collecting duct
Why do blood vessels surround the nephron?
To carry filtered blood and reabsorbed substances away from the tubule
What are the two important arterioles for filtration of blood through the kidney?
Afferent arteriole and efferent arteriole
What happens when the blood flows through the renal artery (it goes into which vessel and then what)?
Goes through afferent arteriole, glomerulus and then efferent arteriole
What is the glomerulus?
Ball of capillaries
What happens to the fluid in the glomerulus?
Efferent squeezes, resulting in high pressure, causing fluid to leak out of the glomerular capillaries
When the fluid leaks from the glomerular capillaries, what does it go through?
Passes through the glomerular basement membrane and enters the the Bowman’s capsule
During selective reabsorption, the filtrate in the tubule consists of what?
Water and small hydrophilic molecules such as sugars, amino acids and urea
What happens to substances that are in the tubule that must be returned to the blood stream during selective reabsorption?
Extracted from the tubule, often via active transport, and picked up by peritubular capillaries
What is the proximal convoluted tubule?
The tubule nearest to Bowman’s capsule where a lot of the reabsorption occurs
Along with solute movement in the proximal convoluted tubule, what else follow?
Water; a lot of water reabsorption occurs in that region
What is the two types of convoluted tubules based on selective reabsorption?
- Proximal convoluted tubule
2. Distal convoluted tubule
What is secretion based on kidney filtration?
Movement of substances into the filtrate usually via active transport
Why is secretion considered a back-up plan?
Not everything that needs to be removed from the blood gets filtered out at the glomerulus
Where does most of the secretion occur?
In the DCT and collecting duct
Where does the adjutants are made to the urine volume and osmolarity before being discarded in the ureter?
In the distal nephron
What does the distal nephron section include?
DCT and collecting duct
What is the distal nephron behavior controlled by?
ADH and Aldosterone
How is the volume of fluid and the solute concentration when the body is dehydrated?
Volume of fluid in blood is low and the solute concentration is high
What happens when the body is dehydrated; what hormone is released to assure you maintain enough water?
Antidiuretic hormone; vasopressin or ADH
What released ADH?
Posterior pituitary
What is diuresis?
Water loss in urine
What does ADH prevent?
Diuresis
How does ADH prevent diuresis?
Increases water reabsorption in the distal nephron
How does the ADH increase water reabsorption in the distal nephron?
Makes it permeable to water
What happens if there isn’t any ADH; how does it prevent water reabsorption in the distal nephron?
Without ADH, it’s impermeable to water
What happens when water is reabsorbed in the filtrate by the distal nephron?
Water flows out of the filtrate into the tissue of the kidney, picked up by the peritubular capillaries and returned to the blood
Why does water tend to flow out of the tubule and into the tissue of the kidney when ADH is present?
Because renal medulla has a very high osmolarity which causes water to exit the tubule by osmosis
Why does alcohol cause people to diurese?
It inhibits ADH secretion by the posterior pituitary
When is aldosterone released?
When the blood pressure is low
What released aldosterone hormone?
Adrenal cortex
What does aldosterone do?
Increases reabsorption of Na+ by the distal nephron
Why does increasing the absorption of sodium by the distal nephron help the blood pressure?
Increased plasma osmolarity, leading to increased thirst and water retention which raises the blood pressure
ADH and Aldosterone work together to:…..?
Increase blood pressure
Where are the bowman’s capsule and proximal convoluted tubule located?
In the renal cortex, the outer layer of the kidney
Where does the proximal convoluted tubule empty in?
The loop of Henle
What is the loop of Henle?
Long loop that digs down into the renal medulla
What is the renal medulla?
The inner part of the kidney
What are the two parts to the loop of Henle?
Descending and ascending limb of the loop of Henle
The descending limb of the loop of Henle is the part that….?
Heads into the medulla
The ascending limp of the loop of Henle is the part that….?
Heads back out towards the cortex
What is the difference between ascending and descending limb of the loop of Henle?
Thin descending limb and thick and thick parts to the ascending limb
What is the structural difference between thick and thin walls of the limbs of the loop of Henle?
Thin are squamous epithelial cells, not very metabolically active; thick means cuboidal which are large thick cells that are busily performing active transport
What happens when the fluid further continues down the loop of Henle?
Becomes the distal convoluted tubule
What does the DCT dump into?
Collecting duct
What example has countercurrent multiplier?
Loop of Henle
Why is the loop of Henley considered a countercurrent multiplier?
Ascending and descending limbs go in opposite directions and have different permeabilities
What is the permeability of the descending limb of the loop of Henle?
Permeable to water but not to ions
What happens when water goes through the descending limb of the loop of Henle?
Water exists the descending limb and flows into the high-osmolarity medullary interstitium
What happens to the filtrate when the water escapes the descending limb of Henle?
Becomes concentrated
What is the permeability of the ascending limb of the loop of Henle?
Not permeable to water but passively loses ions from the high-osmolarity filtrate into the renal medullary interstitium
What is the purpose of the thick ascending limb in the loop of Henle?
Actively transport salt out of the filtrate into the medullary interstitium and the medullary interstitium becomes very salty
Why is it important that the medullary interstitium becomes very salty from the ascending limb losing ions?
Medulla will suck water out of the collecting duct by osmosis whenever it is permeable to water
What is the vasa recta connected to?
Branches of efferent arterioles
What does the loop of the vasa recta help with?
Helps to maintain the high concentration of salt in the medulla
Where is the ascending portion of the vasa recta?
Near the descending limb of the loop of Henle; carry of the water that leaves the descending limb
What does the vasa recta do to the water it absorbs?
Return to the bloodstream any water that is reabsorbed from the filtrate
Which part of the kidney undergoes countercurrent exchange?
Vasa recta
How is the vasa recta an example of countercurrent exchange?
The blood in the vasa recta moves in the opposite direction of the filtrate in the nephron `
What is the glomerular filtration rate dependent on directly? What organ assists with that?
Pressure; the kidney has built-in mechanism to help regulate systemic and local (glomerular) blood pressure
What is the juxtaglomerular apparatus?
A specialized contact point between the afferent arteriole and distal tubule
At the juxtaglomerular apparatus, what are the cells called?
Juxtaglomerular cells
What are the names of the cells in the distal tube called?
Macula densa
What is the purpose of the juxtaglomerular cells?
Are baroreceptors that monitor systemic blood pressure
What happens when there is a decrease in blood pressure?
The JG cells secrete an enzyme called renin into the bloodstream
What does the enzyme renin do, based on assistance with blood pressure?
Catalyzes conversion of angiotensinogen into angiotensin I
What happens to angiotensinogen I; does it maintain its same form during assistance with blood pressure?
Converted into angiotensin II by angiotensin-converting enzyme (ACE) in the lungs
What is angiotensin II and why does it help with low blood pressure?
Powerful vasoconstrictor that immediately raises blood pressure
What other hormone can angiotensin II trigger and how?
Stimulates the release of aldosterone which helps raise blood pressure by increasing sodium retention
What are the purpose of the macula densa cells in the distal tube?
Chemoreceptors and monitor filtrate osmolarity in the distal tubule
What happens when filtrate osmolarity decreases based on renal regulation?
The macula dense cells stimulate JG cells to release renn
What effects can macula densa cells have on vessels itself?
Causes a direct dilation of the afferent arteriole, increasing blood flow to the glomerulus
What organ is essential for maintenance of constant blood pH, based on renal regulation?
The kidney
How does the kidney regulate blood pH?
- pH too high - HCO3 is excreted in the urine
2. pH too low - H+ is excreted
What enzyme is involved in the release of HCO3 and H+ based on kidney regulating blood pH?
Carbonic anhydrase
Where is carbonic anhydrase found?
In epithelial cells throughout the nephron, except squamous cells
What does carbonic anhydrase convert?
Conversion of CO2 into carbonic acid H2CO3 which dissociates into bicarbonate plus a proton
Based on renal regulation, which molecule is usually excreted and absorbed by the kidney?
Protons are secreted and bicarbonate are reabsorbed, amounts adjusted to adjust pH
What is the problem with renal regulation of pH?
Slow
What organ is important in blood pH regulation and how?
Lungs; exhaling excess CO2, lung removes an acid H2CO3 from the blood and raises the PH
What is aldosterone based on its molecule? (Not a peptide hormone but….?)
A steroid
What is the hormone made by the kidney?
Erythrpoietin EPO
From where is aldosterone released?
Adrenal cortex
From where is ADH released?
Posterior pituitary
From where is calcitonin released?
C cells
From where is parathyroid hormone released?
Parathyroid
From where is EP released?
Kidney - erythropoietin
What does aldosterone do and how?
Increase blood pressure; increased sodium reabsorption and K+ secretion
What does ADH do?
Increased water reabsorption and plasma volume
How does ADH increase water reabsorption and plasma volume?
Increases permeability of water in epithelial cells of the distal nephron; water flows out of filtrate and into medley interstitium - the vasa recta returns this water to the blood stream
What does calcitonin do and how?
Causes Ca2+ to be removed from he blood by deposition in the bone, reduced absorption by the gut or excretion in the urine when Ca2+ serum is too high
What does parathyroid do and how?
Opposite of that of calcitonin, increased Ca2+ serum
What does kidney do and how?
Increases synthesis of red blood cells in the bone marrow when blood oxygen content falls
What is the role of vitamins in food?
Serve a catalytic role as enemy cofactors or prosthetic groups
What is the secondary function from the digestive system?
Protection from disease
Where is digestion accomplished?
Gastrointestinal tract (GI/ Digestive tract, alimentary canal or gut
The GI tract muscular tube from the mouth to the anus is derived from what?
Gastrulation during embryogenesis
What is the inside of the gut called?
GI lumen
What is the lining of the GI lumen composed with?
Epithelial cells
What are epithelial cells attached to?
Basement membrane
What is the apical surface of the epithelial cells?
The surface of the epithelial cell which faces into the lumen
What do the apical surface of epithelial cells have in the small intestine that increases surface area?
Microvilli
How are apical surface of epithelial cells operated from extracellular environment?
Separated from the remainder of the cell surface by tight junctions
What is the basolateral surface?
The side and bottom of an epithelial cell form, the surface opposite the lumen
What is mostly responsible for the secretory activity of the GI tract?
Specialized epithelial cells
What is the GI muscle known as and why?
Smooth muscle because of its smooth microscopic appearance
Which organs have striated muscles?
Skeletal and cardiac muscle
What are the names of the two layers of smooth muscle lining the gut?
The longitudinal layer and the circular layer
What is the GI motility?
The rhythmic contraction of GI smooth muscle
What does it mean when said that GI smooth muscle has automaticity?
It contracts periodically without external stimulation due to spontaneous depolarization
What does it mean when said that GI smooth muscle has functional syncytium?
When one cell has an action potential and contracts, the impulse spreads to neighboring cells
What does it mean when said that GI smooth muscle has an enteric nervous system?
The GI tract contains its own massive nervous system; controls GI motility
How can GI motility be influenced?
Increased or decreased by hormonal input
How does the parasympathetic nervous system stimulate motility?
Cause sphincters to relax, allowing food to pass; sympathetic does the opposite
What is the purpose of the GI motility?
- Mixing of food
2. Movement of food down the gut
How is mixing of food accomplished by GI motility?
Disordered contractions of GI smooth muscles
How is movement of food down the GI tract accomplished by GI motility?
Orderly form of contraction known as peristalsis
What is peristalsis?
Orderly form of contraction
How does peristalsis keep food separate?
Prevents food further down from mixing backwards
After peristalsis, which muscle contracts? What happens?
Longitudinal muscle; shortening of the gut so that it is pulled over the food like sock - food moves forward
What is a bolus?
Ball of food moving through the GI tract
What is the enteric nervous system?
Branch of the autonomic nervous system that helps to control digestion via innervation of the GI tract, pancreas and gall bladder
What does the enteric nervous system help with?
Regulate blood flow, gut movements, exchange of fluid from the gut to and from its lumen
How would the parasympathetic and sympathetic nervous systems have effects on the enteric nervous system?
Para: Stimulates enteric branch and stimulate digestion
Symp: Inhibit enteric branch
What are the networks of the enteric nervous system?
Myentric plexus and submucosal plexus
Where is the myentric plexus located?
Between the circular and longitudinal muscle layers
What does the myentric plexus help with?
Helps regulate gut motility
Where is the submucosal plexus located?
Found in the submucosa
What does the submucosal plexus help with?
Regulate enzyme secretion, blood flow and ion/water balance in the lumen
What are the two types of GI secretion?
- Endocrine
2. Exocrine
What is endocrine secretion?
Secrete products into ducts that drain into the GI lumen
What is exocrine secretion?
Ductless glands and secretions are picked up by capillaries and enter bloodstream
Where are acini located?
In the exocrine glands
What are acini?
Specialized epithelial cells
What is the purpose of acini cells?
Secrete products which pass into ducts
What are the primary organs involved in exocrine secretion?
Liver, gallbladder, pancreas, epithelial cells
How is the epithelial cells also included in exocrine secretion?
Release secretion directly into the gut lumen
What are important examples of epithelial cells that are considered exocrine glands?
- Gastric glands in the soma
2. Goblet cells
What is the role of goblet cells?
Secrete mucus
What do the gastric glands secrete?
Acid and pepsinogen
What is pepsinogen?
A protease zymogen
Where can goblet cells be found?
Along the entire GI tract
What is a mucus membrane?
Any body surface covered in mucus
Whenever a meal is to be digested, it must be dissolved in…
Water
What is endocrine secretion accomplished by?
Specialized organs (the pancreas) and by cells in the wall of the gut
What are the two principal cell types in the pancreas?
- Pancreatic acinar cells (Exocrine cells)
2. Islets of Langerhans (Endocrine cells)
What is the role of the mouth in the GI tract?
Fragmentation, lubrication and some enzymatic digestion
How is fragmentation of the mouth accomplished?
Mastication (chewing), Incisors for cutting, capsids for tearing and molars for grinding
What does saliva accomplish?
Some digestion and lubrication
What does saliva contain that hydrolyzes starch and breaks it into fragments?
Salivary amylase (ptyalin)
What is salivary amylase (ptyalin)?
Hydrolyzes starch and breaking it into fragments
What is the smallest fragment yielded by salivary amylase?
Disaccharide; monosaccharide digestion occurs at intestinal brush border
What is the purpose of lingual lipase in saliva?
Fat digestion
Which enzyme assists with protein digestion in saliva?
Trick question: no protein digestion occurs in he mouth
What is the purpose of lysozyme in saliva?
Attacking bacterial cell walls; mouth participates in innate immunity
Why can’t carbohydrates be absorbed in the mouth?
Absorption requires special transmembrane transporters located on the intestinal brush border
The pharynx contains the openings of two tubes; what are they?
- Trachea
2. Esophagus
What is the structure of the trachea and what does it do?
Cartilage-lined tube at the front of the neck which conveys air to and from the lungs
What is the structure of the esophagus and what does it do?
Muscular tube behind the trachea which conveys food and drink from the pharynx to the stomach
What is the epiglottis?
Flat cartilaginous flap that excludes solids and liquids from entering the trachea
What are the muscular rings regulating movement of food through the esophagus?
- Upper esophageal sphincter
2. Lower esophageal sphincter
What is the cardiac sphincter also known as?
Lower esophageal sphincter
What is the purpose of the lower esophageal sphincter?
Prevent reflux from he stomach into the esophagus
What are the three purposes of the stomach?
Partial digestion of food, regulated release of food into the small intestine and destruction of microorganisms
What is the acidity of the GI?
Gastric pH is about 2 due to the secretion of HCl by partial cells located in the gastric mucosa
What are the effects of low gastric pH?
- Destruction of microorganism 2. Acid-catalyzed hydrolysis of many dietary proteins 3. Conversion of pepsinogen to pepsin
What cells release pepsin?
Chief cells in the stomach wall
What does pepsin catalyze?
Catalyzes proteolysis - protein breakdown
Pepsin is secreted as what initially?
Pepsinogen, an inactive precursor that must be converted to the active form (pepsin)
The inactive precursor form is known as…in the GI tract
Zymogen
Most zymogens are activated by…?
Proteolysis - cleavage of protein at a specific site that activates it
Pepsinogen is unique as it is….
Activated by acidic proteolysis instead of proteolytic cleavagge by another enzyme
What is chyme?
Food mixed with gastric secretions
What is the purpose of the pyloric sphincter?
Prevents the passage of food from the stomach into the duodenum
When is the opening of the pyloric sphincter inhibited?
When the small intestine already has a large load of chyme
What happens when there is excess acidity in the duodenum or stretching there?
Inhibits stomach emptying by causing pyloric sphincter to contract
What is the main hormone responsible for the duodenum and stomach sphincters response?
Cholecystokinin
What releases gastrin hormone?
G cells
What does gastrin stimulate?
Stimulates acid and pepsin secretion and gastric motility
What stimulates gastrin secretion?
Food in the stomach and by parasympathetic stimulation
What molecule responds to stomach stretching and gastrin secretion?
histamine
What does histamine do when the gastrin secretion is stimulated?
Binds to parietal cells to stimulate acid release
What does the inhibition of histamine cause based on gastrin secretion?
Results in less gastric activity and allows for ulcers to heal
What are the three parts of the small intestine?
Duodenum, jejunum and ileum
What is the key feature that allows the small intestine to accomplish absorption?
Its large surface area
What features allows for the small intestine to have such a large surface area?
- Length
- Villi
- Microvili
What are villi?
Macroscopic projections in the wall of the small intestines
What are microvilli?
Microvilli foldings of the cell membrane of individual intestinal epithelial cells
What is the brush border?
The lumenal surface of the small intestine
What important structures does the intestinal villus contain?
- Capillaries
- Laceals
- Peyer’s patches
What does the capillaries do in the intestinal villus?
Absorb dietary monosaccharides and amino acids; merge to form the large hepatic portal vein
What are lacteals?
Small lymphatic vessels
What do lacteals do?
Absorb dietary fats
What do the lacteals merge into?
Merge to form large lymphatic vessels
What are Peyer’s patches and where are they located?
Collections of lymphocytes dotting the villi that monitor GI content and confer immunity to gut pathogens and toxins
What are the two ducts that the duodenum empties into?
- Pancreatic duct
2. Common bile duct
What is the pancreatic duct lead to?
Delivers the exocrine secretions of the pancreas (digestive enzymes and bicarbonate)
What is the common bile duct deliver?
Bile
What is bile?
Green fluid containing bile acids, made from cholesterol in the liver and are normally absorbed and recycled
Where are bile stored?
Stored in the gallbladder until it is needed
What is the function of bile?
- Excretion of waste products by the liver
2. Digestion of fats
How does the bile duct and the pancreatic duct empty into the duodenum?
Via the same orifice, known as the sphincter of Oddi
What does duodenal enterokinase cause?
Activates the pancreatic zymogen trypsinogen to trypsin
What are brush border enzymes?
Does their work inside or on the surface of the brush border epithelial cells
What is the role of the brush border enzymes?
To hydrolyze the smallest carbohydrates and proteins into monosaccharides and amino acids
What are the main duodenal hormones?
- Cholecystokinin 2. Secretin 3. Enterogastrone
When is cholecystokinin (CCK) secreted?
In response to fats in the duodenum
What does the CCK cause cholecystokinin?
Causes the pancreas to secrete digestive enzymes, stimulates gallbladder contraction and decreases gastric motility
How does the CCK stimulation helps with dealing with fats in the duodenum?
By digesting them and preventing further stomach emptying
Duodenal hormones are released in response to what?
Response to acid in the duodenum and causes the pancreas to release large amounts of high pH aqueous buffers
What pH aqueous buffer does the pancreas release in response to a stimulation of duodenal hormones?
HCO3- in water
What does releasing HCO3 in water cause, based on pancreatic stimulation?
It neutralizes HCL released b the stomach
How must the pH of the duodenal must be kept?
Must be kept neutral or even slightly basic for pancreatic digestive enzymes function
What does enterogastrone do and what is it?
It is a duodenal hormone and it decreases stomach emptying
