The Digestive and Excretory System Flashcards
What enzyme is responsible for the chemical breakdown of food in the mouth? What does it break down?
Alpha-Amylase: breaks down starch into polysaccharides. Only carbohydrates break down chemically in the mouth. Everything else is broken down physically
What is a sphincter?
A ring of muscle that remains contracted so that there is no opening in the center. The stomach normally remains closed unless cardiac (entrance to the stomach) pyloric sphincter (entrance to the small intestines) opens.
What is the pH inside the stomach?
2
What are the gastric pits?
Deep pits in the stomach with exocrine glands embedded composed of various major stomach cells. Where the four major cell types in the stomach are found and releases the gastric juices
What are the chief cells?
Releases pepsinogen through the exocrine gland in the stomach which is activated due to the acidic environment of the stomach
What is pepsin?
Digestive enzyme in the stomach that breaks down proteins
What are parietal cells? What is distinctive about their form due to their function?
One of the major cells in the stomach that releases HCl through the exocrine gland. Also releases intrinsic factor which helps the ileum absorb the vitamin B12.
Because it takes a lot of energy to transport HCl into the lumen, parietal cells have lots of mitochondria.
How is the HCl transported into the lumen of the stomach? What happens as a result?
Through active transport which requires a lot of energy. Carbonic acid is made inside the cell. H+ goes into the stomach while biocarbonate ion is released to the interstitial side. The net result is that the pH of the stomach is lowered while the blood is raised.
What are the G-cells?
Releases gastrin which cause parietal cells to release HCl
What chemical results in the secretion of cell types in the stomach?
Acetylcholine
Where does the 90% of the digestion and absorption occur?
The small intestine
In the small intestine, where does the most digestion occur and where does the most absorption occur?
Most digestion occurs in the duodenum and the most absorption occurs in the jejunum and ileum.
How is the small intestine well-suited for absorption?
Villi and microvilli. The surface of the villi cells are called enterocytes. These enterocytes have small finger-like projections called microvilli that increase the SA for absorption. The microvilli appear as a fuzzy covering, called the brush border.
What digestive enzymes do brush border covering contain?
Carbohydrate, protein, and nucleotide-digesting enzymes
Dextrinase, maltase, sucrase, lactase, peptidase, nucleosidases
The small intestine is well-suited for absorption. How is the digestion takes place in the small intestine?
Pancreas
How is it that the fluid inside the duodenum is pH 6 while the stomach is pH 2?
Acids from the stomach is neutralized by the bicarbonate ions from the pancreas
The acinar cells of the pancreas release digestive enzymes to the main pancreatic duct which is released into what part of the small intestine?
Duodenum
What are the major pancreatic digestive enzymes released into the small intestine?
trypsin, chymotrypsin, pancreatic amylase, lipase, ribonuclease, and deoxyribonuclease
T/F: All pancreatic digestive enzymes are released as zymogens
True
How is trypsin activated? What does the activated trypsin do?
Activated by enterokinase in the brush border. Activated trypsin activates all other zymogens released from the pancreas
Function of trypsin and chymotrypsin
Degrade proteins into small polypeptides
Function of carboxypolypeptidase
cleaves amino acids from the sides of the peptides broken down by trypsin and chymotrypsin
Function of pancreatic amylase
Very powerful. Degrades proteins into disaccharides and trisaccharides. The brush border enzymes reduce them into monosaccharides to be absorbed.
Main nerve responsible for digestion
Vagus nerve from the parasympathetic nervous system
What makes gastrin to be released more into the stomach?
Distention of the stomach, the presence of polypeptides in the stomach, and the nerve input from the vagus nerve.
Gastrin: site, stimulus, target, and effects
Site: Stomach
Stimulus: ACh release from the vagus nerve, distention of the stomach, and presence of polysaccharides in the stomach
Target: Stomach
Effect: Stimulates production of HCl
Secretin: site, stimulus, target, and effects
The messenger through the secretory passage; tells the pancreas that chyme has arrived and needs to be neutralized, and digested further
Site: Duodenum
Stimulus: Arrival of HCl in chyme
Target: Pancreas
Effects: Stimulates secretion of sodium bicarbonate and digestive enzymes from the pancreas, increase insulin in blood
Gastric inhibitory peptide: site, stimulus, target, and effects
Site: Duodenum
Stimulus: Arrival of fat and protein digestates in chyme
Target: Pancreas and stomach
Effects: Stimulates enzyme secretion in the pancreas and decreases motor activity in the stomach, increases insulin in blood
CCK: site, stimulus, target, and effects
Site: Duodenum
Stimulus: Arrival of fat digestates in chyme
Effects: stimulates enzyme secretion in the pancreas and decreases motor activity in the stomach, increase insulin in blood
What is the function of reducing motility of the stomach by CCK and gastric inhibitory peptide?
To make sure chyme is released slowly into the small intestine so there is more time to get it digested. Fat is more difficult to digest since it needs to be emulsified first.
Large polysaccharides are broken into smaller polysaccharides by what enzyme?
Amylase
The small polysaccharides are broken ultimately into monosaccharides by what enzymes?
Brush border enzymes
How is glucose transported across the apical surface of the enterocyte? How does fructose and galactose go in?
Glucose uses Secondary active transport: Co-transport with Na+
When there is a high concentration of glucose built up, it built up osmotic pressure and falls down with the aqueous solution through the gap junction
Fructose: Facilitated transport
Galactose: similar to glucose
How is Na+ that co-enters with glucose leave the enterocyte and back into the lumen of the intestine?
Primary active transport: Na+/K+ pump
How does the glucose enter the blood (portal vein to the liver) from the enterocyte?
Facilitated transport
Where are the most fructose and galactose converted into glucose?
In the liver
Protein is broken down into polypeptides in the _____ by the enzyme _____
broken down in the stomach by pepsin into polypeptides
Polypeptides are broken down into small polypeptides and amino acids by enzymes _______ in the ______. The small polypeptides and amino acids are broken down into amino acids, dipeptides, and tripeptides by ______.
trypsin and chymotrypsin in the small intestine
the small polypeptides are broken into amino acids, dipeptides, and tripeptides by the brush border enzymes in the small intestine
How are the amino acids, dipeptides, and tripeptides transported across the enterocyte?
by facilitated diffusion. Tripeptide is co-facilitated with Na+
Where and how are the tripeptides and dipeptides broken into individual amino acids?
In the enterocytes by enterocyte enzymes
Where does the digestion of large fat droplet begin and by what enzyme?
In the small intestine by lipase and bile working together
How is fat transported into the enterocytes?
Fat is first broken down into monoglycerides, triglycerides, cholesterol, phospholipid, and fatty acids. The individual constituents then hop onto the micelles to be transported near to the enterocytes. Monoglycerides then hop out of the micelle shuttle and diffuse easily across the plasma membrane (small, non-polar).
How do the individual fat constituents leave the enterocyte and into the lymph fluid?
Series of rearrange and congregation to finally form chylomicrons (sER –> golgi).
Aqueous cellular environment causes re-aggregation of fat: Monoglycerides are rearranged to form triglycerides in the sER and re-aggregate with the phospholipids and cholesterol. These globules move into the golgi and are now called chylomicrons.
The final destination of the chylomicrons entering the lymph system?
The thoracic duct in the neck
First stop for most of the digested fat
The liver
How are the fatty acids transported in the blood?
combine with the protein albumin in the blood to be transported
Most of the lipids in the plasma are in the form of _____
lipoproteins that looks like chylomicrons. Chylomicrons are large lipoproteins.
What proteins stick outside of chylomicrons in the enterocyte?
Apoproteins
What vein carries all of the blood from the digestive system to the liver so that the liver can process the blood before it is re-circulated throughout the rest of the body?
hepatic portal vein
What happens when the liver metabolizes fat or protein for energy?
The acidity of the blood increases
What are the metabolic functions of the liver?
Carbohydrate metabolism: maintenance of normal blood glucose level
Fat metabolism: synthesis of vile from cholesterol, conversion into fat, mobilization for energy (production of ketone bodies)
Protein metabolism: deamination of amino acids, forms urea from ammonia, synthesis of fibrinogen, prothrombin, albumin, and most globulins, and non-essential amino acids.
Detoxification
Storage functions of the liver
blood, glycogen, vitamin storage (A, D, B12, Iron)
Immune functions of the liver
Blood filtration: phagocytosis of bacteria picked up from the intestines
RBC destruction: destroy irregular RBC but most RBC destruction is done by the spleen
What is filtered out in the glomerulus?
large proteins and blood
Where does the most of the reabsorption and secretion take place in the nephron?
Proximal tubules
In the proximal tubules, how are H+ secreted and how is water reabsorbed?
What is the net result of the proximal tubule?
H+ secreted via antiport system (Na+/H+ antiport system)
Water is reabsorbed via osmosis
The net result is that the concentration of solutes in the filtrate is unchanged. The amount of filtrate in the nephron is reduced and the solute composition is altered while the overall concentration of solutes in the filtrate is unchanged.
glomerulus
capillary bed of the kidney where the blood first enters
how is glucose reabsorbed in the proximal tubule?
secondary active transport
T/F reabsorption occurs only via passive transport
F. Reabsorption can be passive or active transport
Permeability of the descending loop of Henle
Permeable to water and impermeable to solutes. Water diffuses out. Solute concentration increases, increasing osmolarity
Permeability of the ascending loop of Henle (the thick portion)
How do the solutes diffuse out in the thick portion? How are they reabsorbed first?
Permeable to solutes. The solutes diffuse out passively first then by active transport.
The thick ascending portion is nearly impermeable to water.
How is an osmolarity gradient established in the medulla?
the single effect
countercurrent multiplier
countercurrent exchanger
What does it mean when the loop of Henle has a counter current flow?
When the filtrate descends down then ascends up the loop of henle, filtrate in the loop of Henle right parallel to it goes in the opposite direction. Vasa recta also has counter current flow but in opposite direction of the loop of Henle surrounding it
The single effect in the ascending loop of Henle
What happens as a result?
active transport of solute in the wall of the thick ascending loop creating a concentration gradient
Equilibration happens in the descending loop. The water flows out to achieve equilibrium.
the net result of the single effect is to dilute filtrate in the ascending limb while concentrating the medulla, and to concentrate filtrate in the descending limb of the loop of Henle.
The counter current multiplier mechanism
the fluid is continually moving through the loop of Henle
Shifting of the filtrate along the loop, magnification of the concentration gradient
What is the purpose of the medulla’s concentration gradient?
Facilitating water reabsorption into the body, and correspondingly, concentrating the urine.
Describe the osmolarity gradient in the medulla with a normal counter current multiplier mechanism
Most concentrated at the bottom. Least concentrated in the upper region near the cortex.
Same in the loop of Henle. Most concentrated at the bottom and least concentrated on top.
Counter current exchanger
Vasa recta - descension and ascension in opposite direction of loop of Henle
meetings the demands of oxygen, nutrient, and waste removal required by the medulla while keeping the counter current multiplier mechanism working
blood descending the capillary enters the more concentrated medulla: water exits and solutes go in to make the capillary just as concentrated
blood ascending the capillary: opposite effect (absorb water and release solutes to become just little bit more concentrated than the surrounding)
delivers nutrients, and water, and removes waste while doing this
function of the concentrated inner medulla
osmotic pressure that “pulls” free water out of the filtrate, concentrating the urine before it leaves the body. The urine can be concentrated because the descending and ascending segments of the Loop of Henle differs in their permeabilities to solutes and water
Distal tubule
resabsorption of Na+ and Ca2+ while secreting H+, K+, and bicarbonate ion
aldosterone - increase number of sodium and potassium transport proteins in the membrane
Collecting tubule - end portion of the distal tubule where ADH acts on (cause water to flow out and filtrate to become more concentrated)
The collecting duct
carries the filtrate into the highly osmotic medulla
where ADH acts on, making water enter the medulla via passive diffusion down its concentration gradient
What is the juxtaglomerular apparatus
secrete renin when the filtrate pressure is too low. monitors filtrate pressure in the distal tubule.
Renin
Renin produces angiotensin 1, 2, 3, stimulating the adrenal cortex to secrete aldosterone. Aldosterone accts on the distal tubule, stimulating the formation of membrane proteins that absorb sodium and secrete potassium to increase blood pressure
When pepsinogen is released from the chief cells, how is it activated?
It is activated by the acidic environment of the stomach, HCl
Pepsin
Break the middle of the protein. Activated by HCl in the stomach
What does the hepatic portal vein lead to from the intestine?
To the liver
Thin descending limb of loop of Henle
Thin squamous epithelium with NO tight junctions
Water permeable
Thick loop of Henle
Reabsorb salutes
Juxtaglomerular apparatus
Increase the glomerular filter ate rate when needed and conserve Na+
Responsible for ARTERIAL RESISTANCE
Macula dense cells in the distal tube filtrate volume
Macula densa cells
Controls the filtrate volume
Renin
Convert angiotensinogen to angiotensin which constricts the efferent arterial for filtrate volume control
Trypsin and chymotrypsin
Break down proteins in the small intestine
Secreted by the pancreas
Break middle of the peptide into di or tri peptides
Exopeptidase
Break down the ends of a peptide in the small intestine
Sinusoids in the liver
Sacs in the liver that store blood
