Vanders Chapter 14.1-14.4 and Chapter 15.6 (liver and kidneys)

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Questions and Answers

Which organ system is primarily responsible for regulating the inorganic ion composition of the internal environment?

Nervous system

Respiratory system

Cardiovascular system

Urinary system (correct)

What is the primary function of the kidneys in relation to blood?

Regulating blood pressure through vasodilation

Synapsing neurotransmitters for nerve function

Processing plasma by removing and sometimes adding substances (correct)

Facilitating the exchange of gases in the lungs

How is the long-term control of acid-base balance primarily achieved in humans?

Through muscle contractions in the gastrointestinal tract

By hormonal regulation affecting the digestive system

By the kidneys, along with the respiratory system (correct)

Through neural reflexes that regulate heart rate

Which mechanism plays a major role in the regulation of body water balance and inorganic ions?

Reflexes altering urine excretion rates Signup and view all the answers

What two processes on the intake side contribute to the body's balance of substances?

Ingestion/absorption and synthesis Signup and view all the answers

Which of the following is NOT a function of the kidneys?

Facilitating nutrient absorption in the intestines Signup and view all the answers

Which term best describes substances that are lost from the body?

Excreted Signup and view all the answers

In which way does the kidney contribute to homeostasis?

By filtering blood and forming urine Signup and view all the answers

What is the primary role of the kidneys in relation to Na+ and Cl− ions?

To balance Na+ and Cl− excretion in relation to dietary intake Signup and view all the answers

Which metabolic waste product is specifically excreted by the kidneys from protein catabolism?

Urea Signup and view all the answers

What is one of the main functions of the kidneys during prolonged fasting?

Synthesize glucose from amino acids Signup and view all the answers

What role does renin play in kidney function?

It influences blood sodium balance and pressure Signup and view all the answers

What is the basic functional unit of the kidney called?

Nephron Signup and view all the answers

Which structure is NOT associated with the kidney's filtration process?

Ureter Signup and view all the answers

What is the consequence of kidney failure in relation to metabolic wastes?

Accumulation of toxic metabolic wastes in the body Signup and view all the answers

Which ion's excretion is NOT primarily controlled by the kidneys?

Fe2+ Signup and view all the answers

How do the kidneys participate in the regulation of acid-base balance?

By excreting hydrogen ions and absorbed bicarbonate Signup and view all the answers

What structural feature of the kidney is responsible for urine flowing into the ureter?

Renal pelvis Signup and view all the answers

Which hormone produced by the kidneys plays a critical role in red blood cell production?

Erythropoietin Signup and view all the answers

What is meant by the term 'retroperitoneal' in relation to the kidneys?

They lie just behind the peritoneum lining of the cavity Signup and view all the answers

Which component of the nephron is directly responsible for filtering blood?

Renal corpuscle Signup and view all the answers

What is the main purpose of the renal corpuscle's structure?

To create an efficient sieve for ultrafiltration Signup and view all the answers

Which layer is NOT part of the filtration barrier separating blood in the glomerulus from fluid in Bowman’s space?

Smooth muscle layer Signup and view all the answers

What happens to the kidneys' excretion of ions when the body is low on Na+ and Cl−?

The kidneys reduce the excretion of these ions Signup and view all the answers

Which part of the nephron is primarily responsible for the initial filtration of blood?

Renal corpuscle Signup and view all the answers

What percentage of plasma typically filters into Bowman’s capsule from the glomerulus?

20% Signup and view all the answers

What characteristic of podocytes contributes to their function in the filtration barrier?

They have numerous foot processes Signup and view all the answers

Which structure ultimately receives the filtrate after it leaves the renal corpuscle?

Distal convoluted tubule Signup and view all the answers

What feature distinguishes juxtamedullary nephrons from cortical nephrons?

Long loops of Henle Signup and view all the answers

What is the primary function of the efferent arteriole in the renal corpuscle?

To remove filtered blood from the glomerulus Signup and view all the answers

Which component of the renal corpuscle is described as a 'fluid-filled capsule'?

Bowman's capsule Signup and view all the answers

What type of capillaries compose the glomerulus?

Fenestrated capillaries Signup and view all the answers

What role does the macula densa play within the nephron?

Sensing sodium concentration Signup and view all the answers

What does the term 'Bowman's space' refer to?

The space between the glomerulus and capsule Signup and view all the answers

What distinguishes the peritubular capillaries from the vasa recta?

Location in the cortex Signup and view all the answers

What happens to the remaining blood after approximately 20% has filtered into Bowman’s capsule?

It exits through the efferent arteriole Signup and view all the answers

What is the primary function of the podocytes in the kidney?

To filter blood particles based on size Signup and view all the answers

Which component of the nephron is primarily responsible for the reabsorption of water?

Collecting duct Signup and view all the answers

What happens to substances larger than 8 nm in diameter during filtration?

They are completely retained in the bloodstream Signup and view all the answers

What comprised the glomerular filtration membrane?

Capillary endothelium, basement membrane, and podocytes Signup and view all the answers

How do juxtamedullary nephrons contribute to kidney function?

They are primarily involved in urine concentration Signup and view all the answers

Which structure connects the glomerular capillaries to the peritubular capillaries?

Efferent arteriole Signup and view all the answers

What is filtered first during urine formation?

Urea Signup and view all the answers

What is the function of mesangial cells in the kidney?

To structurally support glomerular capillaries Signup and view all the answers

In what way does the kidney's vascular structure differ from typical circulatory systems?

Two sets of capillaries with two sets of arterioles Signup and view all the answers

What is the role of the macula densa?

It regulates the glomerular filtration rate Signup and view all the answers

Why are some polypeptides filtered into Bowman’s capsule?

They are smaller than 8 nm Signup and view all the answers

How does the renal cortex differ from the renal medulla?

The cortex contains glomerular capillaries whereas the medulla only contains tubules Signup and view all the answers

What is primarily transported from the distal convoluted tubule?

Electrolytes Signup and view all the answers

What is the process called when substances move from the tubular lumen to the peritubular capillary plasma?

Reabsorption Signup and view all the answers

In which situation will a substance be completely reabsorbed by the kidneys?

When it is essential for health Signup and view all the answers

Which of the following correctly summarizes the amount of substance excreted in urine?

Amount filtered plus amount secreted minus amount reabsorbed Signup and view all the answers

What happens when a person who is normally hydrated drinks excessive amounts of water?

Tubular reabsorption of water decreases Signup and view all the answers

Which of the following substances would most likely undergo tubular secretion?

Toxins Signup and view all the answers

How does the rate of renal processes such as filtration and reabsorption vary?

They are dependent on hormonal control Signup and view all the answers

What occurs to a substance that is both filtered and secreted but not reabsorbed?

It is excreted in the urine Signup and view all the answers

To what extent is a substance that is neither reabsorbed nor secreted excreted from the body?

Completely excreted Signup and view all the answers

What is referred to as the ultrafiltrate?

Liquid with all substances except proteins Signup and view all the answers

Which of the following statements is true regarding the movement of substances in the renal tubule?

Reabsorption and secretion occur simultaneously for most substances Signup and view all the answers

Why might the body completely reabsorb substance Z?

It is crucial for maintaining homeostasis Signup and view all the answers

What primarily explains the exclusion of plasma proteins from the glomerular filtrate?

The renal corpuscles restrict the movement of high-molecular-weight substances Signup and view all the answers

What is the role of renal tubular cells in relation to substances in the tubular fluid?

They can both metabolize and produce substances Signup and view all the answers

Which factor contributes most to opposing glomerular filtration?

Hydrostatic pressure in Bowman’s space Signup and view all the answers

What is the relationship between glomerular filtration and the body’s regulation of substance levels?

Regulation can involve adjusting filtration rates Signup and view all the answers

How does the osmotic force in the glomerular capillary plasma influence filtration?

It opposes filtration due to the concentration of proteins Signup and view all the answers

What process leads to the clearance of a toxic substance from the plasma?

Filtration combined with tubular secretion Signup and view all the answers

What does the net glomerular filtration pressure calculate as?

PGC - PBS - πGC Signup and view all the answers

What is the glomerular capillary hydrostatic pressure (PGC) typically at?

60 mmHg Signup and view all the answers

How does the movement of water influence the osmotic force in glomerular capillaries?

Water movement increases protein concentration in the capillaries Signup and view all the answers

Which of the following statements is true regarding low-molecular-weight substances bound to plasma proteins?

They cannot be filtered due to their binding Signup and view all the answers

Which physiological principle underlies the filtration process in the kidneys?

Starling forces governing fluid movement Signup and view all the answers

What role does the renal artery play in glomerular capillary filtration pressure?

Its shorter length and greater radius increases blood flow Signup and view all the answers

What effect would an increase in plasma albumin have on the glomerular filtration rate?

Decreases the filtration rate due to increased osmotic pressure Signup and view all the answers

What best describes why the concentration of protein in Bowman’s space is considered zero?

Filtration pathways are designed to exclude proteins Signup and view all the answers

Which of these substances usually passes freely into the glomerular filtrate?

Low-molecular-weight substances Signup and view all the answers

During glomerular filtration, which component of pressure opposes the filtration process?

Osmotic force due to plasma proteins Signup and view all the answers

Which condition would most likely cause a reduction in net glomerular filtration pressure?

Increased hydrostatic pressure in Bowman’s space Signup and view all the answers

What factors primarily determine the glomerular filtration rate (GFR)?

Net filtration pressure, membrane permeability, and surface area Signup and view all the answers

What happens to the hydrostatic pressure in the glomerular capillaries when the efferent arteriole is constricted?

It increases due to blood backing up Signup and view all the answers

Which statement is correct regarding the control of glomerular filtration rate (GFR)?

Both afferent and efferent arterioles can influence it through constriction or dilation Signup and view all the answers

What is the primary role of mesangial cells in the glomeruli?

Decrease the surface area of capillaries Signup and view all the answers

What does the term 'filtered load' refer to?

The amount of a specific substance filtered into Bowman’s space based on GFR Signup and view all the answers

If the glomerular filtration rate (GFR) is 180 L/day and plasma glucose concentration is 1 g/L, what is the filtered load of glucose?

180 g/day Signup and view all the answers

What is a likely consequence of a decrease in GFR?

Accumulation of filtration waste in blood Signup and view all the answers

How does physiological regulation affect GFR?

It allows for rapid adjustments based on need through neural and hormonal mechanisms Signup and view all the answers

Which statement best describes the permeability of glomerular capillaries compared to other capillaries?

They are much more permeable to fluid Signup and view all the answers

What would result from simultaneous constriction of both afferent and efferent arterioles?

No significant change in PGC Signup and view all the answers

Which of the following substances is completely reabsorbed in a healthy kidney?

Glucose Signup and view all the answers

Which plasma component is typically filtered and reabsorbed incompletely?

Urea Signup and view all the answers

What distinguishes reabsorption rates that can be physiologically regulated from those that cannot?

Physiological control mechanisms for substances Signup and view all the answers

What role does proper functioning of the kidneys play in regulating the internal environment?

They filter and utilize large volumes of plasma to maintain homeostasis Signup and view all the answers

What is the average GFR for a 70 kg person?

125 mL/min Signup and view all the answers

In the process of tubular reabsorption, movement from tubular lumen to interstitial fluid primarily occurs through which mechanisms?

Diffusion and mediated transport Signup and view all the answers

How is urea reabsorbed in the proximal tubule despite being a waste product?

Facilitated by the reabsorption of water Signup and view all the answers

Which physiological mechanism could cause an increase in GFR?

Dilation of the afferent arteriole Signup and view all the answers

Which statement is correct regarding the reabsorption of glucose in the kidneys?

It is coupled with the reabsorption of sodium. Signup and view all the answers

What is the phenomenon when the transport maximum (Tm) is exceeded for glucose in the renal tubule?

Glucosuria Signup and view all the answers

What role does the apical membrane play in the reabsorption process?

It separates the tubular lumen from the cell interior. Signup and view all the answers

What occurs after substances reach the interstitial fluid during reabsorption?

They move into peritubular capillaries through diffusion and bulk flow. Signup and view all the answers

Which factor plays a significant role in determining the transport maximum (Tm) for glucose?

The saturation of membrane transport proteins Signup and view all the answers

In individuals with poorly controlled diabetes mellitus, at what plasma glucose concentration does glucosuria typically start to occur?

200 mg/100 mL Signup and view all the answers

Which of the following components has a high percentage of reabsorption, close to 100%?

Glucose Signup and view all the answers

What is the function of tubular secretion in the kidneys?

Move substances from blood into the tubular lumen Signup and view all the answers

What is the primary mechanism for the reabsorption of most organic nutrients in the kidneys?

Simple diffusion based on concentration gradients Signup and view all the answers

Which substances are primarily secreted by the renal tubules?

H+ and K+ Signup and view all the answers

What mechanism is primarily responsible for sodium reabsorption across the basolateral membrane?

Na+/K+-ATPases pump Signup and view all the answers

How does sustained hyperglycemia affect renal glucose reabsorption?

It leads to increased glucose excretion. Signup and view all the answers

What is an essential characteristic of mediated transport in tubular reabsorption?

It involves transport proteins in cellular membranes. Signup and view all the answers

Which molecules are commonly subject to tubular reabsorption in the proximal tubule?

Glucose and amino acids Signup and view all the answers

What is the primary benefit of tubular reabsorption for the body?

It conserves essential nutrients and minimizes waste. Signup and view all the answers

Which type of transport is involved in tubular secretion?

Active transport and facilitated diffusion Signup and view all the answers

How does the body respond to decreased water intake regarding reabsorption?

Increases water reabsorption in the kidneys. Signup and view all the answers

Which process occurs when solutes are transported from the blood into the tubular lumen?

Secretion Signup and view all the answers

What effect does high plasma levels of vitamin C have on reabsorption in the kidneys?

It can lead to increased excretion when Tm is surpassed. Signup and view all the answers

What is the main regulation mechanism for renal transport proteins?

Hormonal and paracrine factors Signup and view all the answers

Why might individuals who ingest large quantities of vitamin C see it in their urine?

It exceeds the reabsorptive capacity of the tubules. Signup and view all the answers

What happens to the kidneys when the filtered load of glucose is increased significantly?

They may start to excrete glucose in urine. Signup and view all the answers

What characterizes the renal tubules during fasting?

They produce and release glucose into the bloodstream. Signup and view all the answers

What role do goblet cells play in the small intestine?

Secrete mucus for lubrication Signup and view all the answers

How does the structure of the small intestine maximize its absorptive capacity?

By incorporating circular folds, villi, and microvilli Signup and view all the answers

What is the approximate total surface area of the human small intestine?

About 250 to 300 square meters Signup and view all the answers

What is the function of lacteals in the small intestine?

To transport absorbed fats to the general circulation Signup and view all the answers

During which segment of the small intestine is most of the chyme digested and absorbed?

Duodenum and part of the jejunum Signup and view all the answers

What is one of the main causes of water movement into the lumen of the small intestine?

Secretion of mineral ions like Na+ and Cl− Signup and view all the answers

What occurs in the event of a portion of the small intestine being removed?

The remaining tissues often increase their absorptive capacities Signup and view all the answers

What is the primary function of the secretions from the pancreas in the context of the small intestine?

Aid in the digestion of macronutrients Signup and view all the answers

What type of epithelial cells are primarily responsible for nutrient absorption in the small intestine?

Simple columnar epithelium with microvilli Signup and view all the answers

How does chyme's hypertonic nature affect the small intestine?

By enhancing water movement into the lumen Signup and view all the answers

What is the main reason pancreatic bicarbonate secretion is critical during digestion?

It neutralizes the acidity of chyme. Signup and view all the answers

What mechanism enables the absorption of monosaccharides and amino acids in the small intestine?

Secondary active transport driven by Na+ ions Signup and view all the answers

The pancreatic acinar cells secrete which type of compounds?

Proteolytic and non-proteolytic enzymes. Signup and view all the answers

Where does bile produced by the liver go between meals?

It is stored in the gallbladder Signup and view all the answers

How is bicarbonate primarily transported into the pancreatic duct lumen?

Using a Cl−/HCO 3− exchanger. Signup and view all the answers

What is the role of enterokinase in the activation of pancreatic enzymes?

It cleaves peptide fragments from zymogens. Signup and view all the answers

What is the purpose of mucus secreted in the small intestine?

To lubricate and protect the epithelial cells Signup and view all the answers

The secretion of pancreatic enzymes is primarily stimulated by which hormones?

Secretin and CCK. Signup and view all the answers

What happens to pancreatic secretions in cases of cystic fibrosis?

Pancreatic secretions become thick and less fluid. Signup and view all the answers

Which of the following enzymes secreted by the pancreas is responsible for breaking down triglycerides?

Lipase. Signup and view all the answers

What initiates the secretion of secretin from enteroendocrine cells in the intestine?

Increased acidity in the duodenum. Signup and view all the answers

What is the main function of trypsin once it is activated?

To activate other proteolytic enzymes. Signup and view all the answers

How do Na+ and water move into the pancreatic ducts according to the content provided?

Via a paracellular route due to an electrochemical gradient. Signup and view all the answers

Which pancreatic enzyme is released in active form?

Amylase. Signup and view all the answers

What is the significance of zymogens in pancreatic secretions?

They prevent autodigestion of pancreatic cells. Signup and view all the answers

What leads to the recycling of chloride ions in pancreatic duct cells?

Cystic fibrosis transmembrane conductance regulator (CFTR). Signup and view all the answers

What pathway do fats and fat-soluble nutrients take after absorption across the intestinal epithelium?

They first enter the lymphatic system before reaching the bloodstream. Signup and view all the answers

How does the blood leaving the small intestine differ from blood leaving other organs like the pancreas or large intestine?

It first travels through the hepatic portal vein to the liver. Signup and view all the answers

What significant processing occurs in the liver after nutrients are absorbed from the intestinal capillaries?

Metabolic regulation influenced by insulin and glucagon. Signup and view all the answers

Which of the following is processed by the liver due to the portal circulation?

Products of carbohydrate and protein digestion. Signup and view all the answers

What is the primary function of the hepatic portal system?

To deliver nutrients absorbed in the abdominal organs for liver processing. Signup and view all the answers

What is the primary site for the completion of starch digestion in the digestive system?

Small intestine Signup and view all the answers

Which carbohydrate is absorbed directly via facilitated diffusion in the small intestine?

Fructose Signup and view all the answers

What enzyme initiates protein digestion in the stomach?

Pepsin Signup and view all the answers

What is the primary pigment found in bile that contributes to its yellow color?

Bilirubin Signup and view all the answers

What is the main digestive enzyme responsible for fat digestion in the small intestine?

Pancreatic lipase Signup and view all the answers

During protein absorption, how are short chains of two or three amino acids primarily absorbed?

Secondary active transport Signup and view all the answers

What triggers the relaxation of the sphincter of Oddi to allow bile flow into the duodenum?

Release of cholecystokinin (CCK) Signup and view all the answers

Which cell type primarily secretes bile salts and cholesterol?

Hepatocytes Signup and view all the answers

Which monosaccharide is produced by the digestion of sucrose?

Glucose Signup and view all the answers

How does the liver reclaim bile salts after they are secreted into the duodenum?

From hepatic portal blood Signup and view all the answers

Which process allows the absorption of larger peptides across the intestinal epithelium?

Endocytosis and exocytosis Signup and view all the answers

What is primarily responsible for the extraction of fatty acids from triglycerides during digestion?

Pancreatic lipase Signup and view all the answers

What role do bacterial enzymes play in the intestinal tract regarding bilirubin?

They modify bilirubin to give feces their characteristic color. Signup and view all the answers

What type of transporter is primarily used by glucose and galactose for absorption in the small intestine?

Sodium-glucose cotransporter Signup and view all the answers

What percentage of bile salts is typically lost in feces?

5% Signup and view all the answers

What is the significance of the hepatic portal vein?

It delivers nutrients from the intestine to the liver. Signup and view all the answers

What is the typical range of protein intake in an average American diet?

60 to 90 g Signup and view all the answers

Which type of carbohydrate is largely not absorbed during digestion?

Polysaccharides Signup and view all the answers

What physiological condition increases the secretion of bicarbonate-rich solutions by bile duct epithelial cells?

Presence of acidic chyme from the stomach Signup and view all the answers

What type of substances are primarily absorbed as dipeptides and tripeptides?

Proteins Signup and view all the answers

Which of the following is NOT a component actively secreted by hepatocytes into bile?

Lactose Signup and view all the answers

What is the approximate percentage of carbohydrates digested and absorbed in the first part of the small intestine?

More than 95% Signup and view all the answers

Which mechanism primarily helps in the absorption of glucose and galactose from the intestinal lumen?

Cotransport with Na+ via SGLT Signup and view all the answers

Which enzyme further digests peptide fragments in the small intestine?

Chymotrypsin Signup and view all the answers

What is the function of the gallbladder in relation to bile?

It concentrates bile between meals. Signup and view all the answers

What impact does the contraction of the gallbladder have on bile flow?

Increases bile flow into the duodenum. Signup and view all the answers

What is primarily absorbed by facilitated diffusion from the intestinal lumen?

Fructose Signup and view all the answers

What triggers the secretion of CCK in the digestive process?

Fatty acids and amino acids in the duodenum Signup and view all the answers

What condition leads to the formation of gallstones?

High cholesterol levels in the bile Signup and view all the answers

What role does HCO3− play in the digestive system?

It neutralizes stomach acid in the small intestine. Signup and view all the answers

Which component of bile is primarily responsible for solubilizing dietary fats?

Bile salts Signup and view all the answers

The enterohepatic circulation involves the recycling of which substance?

Bile salts Signup and view all the answers

During which digestive phase do pancreatic secretions primarily get stimulated?

Intestinal phase Signup and view all the answers

What happens to the bile salts that are not reabsorbed during digestive processes?

They are excreted in feces. Signup and view all the answers

What is one of the key functions of the hepatocytes in the liver?

To store glucose as glycogen Signup and view all the answers

Which of the following substances is primarily involved in maintaining cholesterol homeostasis?

Bile salts Signup and view all the answers

What component of bile is synthesized in the liver and plays a role in emulsifying fats?

Bile salts Signup and view all the answers

What initiates reflexes that increase pancreatic enzyme and bicarbonate secretion?

Intestinal acid and fatty acids Signup and view all the answers

Which liver structure brings oxygenated blood to the liver?

Hepatic artery Signup and view all the answers

What is a major consequence of dietary fiber on bile salts?

Sequesters bile salts, reducing cholesterol absorption Signup and view all the answers

What is the term for the pathway that describes the recycling of bile salts from the intestine to the liver?

Enterohepatic circulation Signup and view all the answers

How are amino acids primarily absorbed into the cytosol of intestinal cells?

Cotransport with Na+ Signup and view all the answers

What is the primary function of colipase during fat digestion?

To bind lipase to lipid droplet surfaces Signup and view all the answers

What primarily facilitates the breakdown of large lipid droplets into smaller ones?

Mechanical disruption by gastrointestinal motility Signup and view all the answers

What structural feature of bile salts allows them to prevent lipid droplet reaggregation?

Their amphipathic properties Signup and view all the answers

What is the result of emulsification in the digestive process?

Increase in surface area for lipase action Signup and view all the answers

Which components are found in micelles that aid in fat absorption?

Bile salts, fatty acids, and cholesterol Signup and view all the answers

What is the primary energy source for the absorption processes of amino acids and small peptides?

ATP from Na+/K+-ATPase pumps Signup and view all the answers

What is a key characteristic of the chemical structure of phospholipids?

A charged phosphate group attached to glycerol Signup and view all the answers

What happens to fatty acids and monoglycerides in the micellar state?

They remain in solution and can be absorbed Signup and view all the answers

What role do peptidases play in protein digestion within the intestine?

They catabolize small peptides to amino acids Signup and view all the answers

What is the correct order of digestion for triglycerides in the digestive system?

Triglycerides to monoglycerides and fatty acids Signup and view all the answers

What is the main function of the brush border in the intestinal epithelium?

To increase surface area for absorption Signup and view all the answers

How do bile salts facilitate fat absorption beyond emulsification?

By enabling the formation of micelles Signup and view all the answers

What role do micelles play in lipid absorption in the intestines?

They aggregate fatty acids and monoglycerides to stay soluble. Signup and view all the answers

Which component of fat digestion is primarily resynthesized in the smooth endoplasmic reticulum of epithelial cells?

Triglycerides Signup and view all the answers

Why can't chylomicrons directly enter blood capillaries after absorption?

The basement membrane provides a barrier to large particles. Signup and view all the answers

What type of vitamins follow the same absorption pathway as lipids in the intestine?

Fat-soluble vitamins Signup and view all the answers

What is the major consequence of impaired bile secretion in relation to nutrient absorption?

Decreased absorption of fat-soluble vitamins Signup and view all the answers

Which protein binds to vitamin B12 for its absorption in the ileum?

Intrinsic factor Signup and view all the answers

What is the primary purpose of amphipathic proteins that coat chylomicrons?

To keep chylomicrons soluble in blood Signup and view all the answers

What is a direct result of celiac disease regarding nutrient absorption?

Decreased intestinal surface area for absorption Signup and view all the answers

Which form of anemia is associated with malabsorption of vitamin B12?

Pernicious anemia Signup and view all the answers

What mechanism is primarily responsible for vitamin B12 absorption in the ileum?

Endocytosis Signup and view all the answers

What pathway do triglycerides take after being resynthesized in intestinal epithelial cells?

Into lacteals and then lymphatic vessels Signup and view all the answers

What is the role of the Golgi apparatus in fat absorption?

It processes lipids before secretion. Signup and view all the answers

What physiological process ensures the availability of fatty acids for absorption?

Replenishing micelles through digestion Signup and view all the answers

Which of the following lipids are NOT typically included in the composition of chylomicrons?

Glucose Signup and view all the answers

What can interfere with the absorption process of fat-soluble vitamins?

Impairment of bile secretion Signup and view all the answers

What percentage of water absorbed in the small intestine passes on to the large intestine?

20% Signup and view all the answers

What role does Na+ play in the absorption of water in the small intestine?

It actively creates osmotic gradients for water absorption. Signup and view all the answers

What happens to iron that is not bound to ferritin in the intestinal epithelial cells?

It is released into the blood bound to transferrin. Signup and view all the answers

Which factor reduces the absorption of iron from egg yolk compared to liver?

Presence of phosphates binding the iron in egg yolk. Signup and view all the answers

How does the body regulate iron absorption based on its iron stores?

By increasing transcription of the ferritin gene when iron stores are high. Signup and view all the answers

What complication arises from very large iron ingestion that overwhelms body regulation mechanisms?

Hemochromatosis Signup and view all the answers

What is the fate of iron absorbed by the intestinal epithelial cells when ferritin levels are low?

More iron is released into the bloodstream. Signup and view all the answers

What components are specifically involved in the absorption of trace metals?

Cellular storage proteins and plasma carrier proteins. Signup and view all the answers

What is the primary function of ferritin in intestinal epithelial cells?

To act as an iron storage complex. Signup and view all the answers

Why does iron accumulate in tissues when excess iron is ingested?

Iron cannot be excreted sufficiently once in the bloodstream. Signup and view all the answers

What does the hepatic portal vein do?

Conducts blood from digestive organs to the liver. Signup and view all the answers

What is the role of chylomicrons in fat absorption?

They transport absorbed fats through the bloodstream. Signup and view all the answers

What happens to fat droplets in the intestinal lumen during fat absorption?

They form micelles for absorption. Signup and view all the answers

What major component does not play a role in the absorption of water in the small intestine?

Surface area of the stomach. Signup and view all the answers

Study Notes

Renal Functions

Kidneys regulate water concentration, inorganic ion composition, acid-base balance, and fluid volume of the internal environment.
Kidneys excrete metabolic waste products like urea, uric acid, creatinine, and end products of hemoglobin breakdown into urine.
Kidneys remove foreign chemicals and their metabolites.
Kidneys synthesize glucose during prolonged fasting.
Kidneys release hormones: erythropoietin, renin, and 1,25-dihydroxyvitamin D.

Kidney Structure and Urinary System

Kidneys are retroperitoneal, located behind the peritoneum.
Urine flows from kidneys through ureters to the bladder and then is eliminated via the urethra.
Kidney consists of an outer renal cortex and an inner renal medulla.
Kidney is divided into nephrons, each consisting of a renal corpuscle and a tubule.
Renal corpuscle filters blood, producing a filtrate free of cells, larger polypeptides, and proteins.
Tubule modifies the filtrate by adding or removing substances.
Fluid at the end of each nephron combines in collecting ducts to form urine.

Renal Corpuscle

Glomerulus, a tuft of interconnected capillary loops, is surrounded by Bowman's capsule.
Afferent arteriole supplies blood to the glomerulus, and efferent arteriole carries blood away.
About 20% of plasma filters into Bowman's capsule.
Filtration barrier consists of three layers: (1) capillary endothelium, (2) basement membrane, and (3) podocyte foot processes.
Mesangial cells surround glomerular capillary loops, their function is yet to be discussed.

Renal Tubule & Collecting Duct System

Proximal tubule (consisting of the convoluted and straight tubule) drains Bowman's capsule.
Loop of Henle is a hairpin-shaped loop with descending and ascending limbs.
Distal convoluted tubule connects to the collecting-duct system (cortical and medullary collecting ducts).
Collecting-duct system merges with other nephrons, ultimately draining urine into the renal pelvis through medullary collecting ducts.

Regional Differences in the Kidney

Cortex contains all the renal corpuscles.
Loops of Henle extend from the cortex into the medulla.
Medullary collecting ducts pass through the medulla to the renal pelvis.
Peritubular capillaries surround the tubule in the cortex.

Types of Nephrons

Juxtamedullary nephrons have a renal corpuscle close to the cortical-medullary junction and long loops of Henle that penetrate deep into the medulla.
Cortical nephrons have renal corpuscles in the outer cortex and short or absent loops of Henle.

Juxtaglomerular Apparatus (JGA)

Ascending limb of each loop of Henle passes between the afferent and efferent arterioles.
Macula densa is a patch of cells in the ascending limb.
Juxtaglomerular (JG) cells are secretory cells in the afferent arteriole.
JGA plays a role in regulating filtration rate. ### Basic Renal Processes
Urine formation begins with the filtration of plasma from the glomerular capillaries into Bowman's space.
The process is called glomerular filtration and the filtrate is called glomerular filtrate.
The filtrate is cell-free and contains all substances except larger proteins in the same concentration as plasma.
During its passage through the tubules, the filtrate's composition is altered by movements of substances from tubules to peritubular capillaries, and vice versa.
Movements from tubular lumen to peritubular capillary plasma are called tubular reabsorption.
Movements in the opposite direction are called tubular secretion.
Tubular secretion can also denote the movement of a solute from the cell interior to the lumen in the cases when the kidney tubular cells themselves generate the substance.
A substance can gain entry to the tubule and be excreted in the urine by glomerular filtration or tubular secretion or both.
The amount of any substance excreted in the urine is equal to the amount filtered plus the amount secreted minus the amount reabsorbed.
Not all processes—filtration, secretion, and reabsorption—apply to all substances.
Important solutes like glucose are completely reabsorbed, whereas most toxins are secreted and not reabsorbed.
About 20% of the plasma that enters the glomerular capillaries is filtered into Bowman's space.
This filtrate, which contains X, Y, and Z in the same concentrations as in the capillary plasma, enters the proximal tubule and begins to flow through the rest of the tubule.
Assume that the tubule can secrete 100% of peritubular capillary substance X into the tubular lumen but cannot reabsorb X.
The plasma that originally entered the renal artery is cleared of all of its substance X, which leaves the body via the urine.
Assume that the tubule can reabsorb but not secrete Y and Z.
The amount of Y reabsorption is moderate so that some of the filtered material is not reabsorbed and escapes from the body.
For Z, however, the reabsorptive mechanism is so powerful that all the filtered Z is reabsorbed back into the plasma.
Therefore, no Z is lost from the body.
A specific combination of filtration, tubular reabsorption, and tubular secretion applies to each substance in the plasma.
The rates at which these processes proceed are subject to physiological control.
By triggering changes in the rates of filtration, reabsorption, or secretion whenever the amount of a substance in the body is higher or lower than the normal limits, homeostatic mechanisms can regulate the substance’s bodily balance.
It is important to stress that not all these processes—filtration, secretion, and reabsorption—apply to all substances.
Important solutes like glucose are completely reabsorbed, whereas most toxins are secreted and not reabsorbed.

### Glomerular Filtration

Glomerular filtrate—that is, the fluid in Bowman’s space—normally contains no cells but contains all plasma substances except proteins in virtually the same concentrations as in plasma.
The filtration pathways in the corpuscular membranes are negatively charged, so they oppose the movement of these plasma proteins, most of which are also negatively charged.
The only exceptions to the generalization that all nonprotein plasma substances have the same concentrations in the glomerular filtrate as in the plasma are certain low-molecular-weight substances that would otherwise be filterable but are bound to plasma proteins and therefore not filtered.

### Forces Involved in Filtration

Filtration across capillaries is determined by opposing Starling forces.
The glomerular capillary hydrostatic pressure (PGC) is a force favoring filtration.
The fluid in Bowman's space exerts a hydrostatic pressure (PBS) that opposes this filtration.
Another opposing force is the osmotic force (πGC) that results from the presence of protein in the glomerular capillary plasma.
The osmotic force in Bowman’s space (πBS) is zero.

### Rate of Glomerular Filtration

The volume of fluid filtered from the glomeruli into Bowman’s space per unit time is known as the glomerular filtration rate (GFR).
GFR is determined not only by the net filtration pressure but also by the permeability of the corpuscular membranes and the surface area available for filtration.
The glomerular capillaries are much more permeable to fluid than most other capillaries.
The net glomerular filtration pressure causes massive filtration of fluid into Bowman's space.
In a 70 kg person, the GFR averages 180 L/day (125 mL/min).
The kidneys filter the entire plasma volume about 60 times a day.

### Tubular Reabsorption

There are at least three important conclusions we can draw from this table:
- The filtered loads are enormous, generally larger than the total amounts of the substances in the body.
- Reabsorption of waste products is relatively incomplete (as in the case of urea), so that large fractions of their filtered loads are excreted in the urine.
- Reabsorption of most useful plasma components, such as water, inorganic ions, and organic nutrients, is relatively complete so that the amounts excreted in the urine are very small fractions of their filtered loads.
An important distinction should be made between reabsorptive processes that can be controlled physiologically and those that cannot.
The kidneys do not regulate the plasma concentrations of these organic nutrients. Rather, the kidneys merely maintain whatever plasma concentrations already exist.
The kidneys have powerful mechanisms to reclaim useful substances from tubular fluid while simultaneously allowing waste products to be excreted.
If water intake is decreased, the kidneys can increase water reabsorption to minimize water loss.

Tubular Reabsorption

Tubular reabsorption moves substances from the tubular lumen to interstitial fluid.
This process does not occur by bulk flow due to insufficient pressure differences and limited permeability of tubular membranes.
Two processes are involved: diffusion and mediated transport.
Diffusion: reabsorption of substances across tight junctions connecting tubular epithelial cells.
Mediated Transport: involves transport proteins in the plasma membranes of tubular cells.
Final step in reabsorption is the movement of substances from the interstitial fluid into peritubular capillaries via diffusion and bulk flow.

Reabsorption by Diffusion

Urea reabsorbed by the proximal tubule is an example of passive reabsorption by diffusion.
Water reabsorption in the proximal tubule increases urea concentration in the tubular fluid, creating a concentration gradient.
Urea diffuses down this gradient from the tubular lumen to the peritubular capillary.

Reabsorption by Mediated Transport

Many solutes are reabsorbed by primary or secondary active transport.
Transcellular epithelial transport: substances cross the apical membrane, diffuse through the cytosol, and cross the basolateral membrane.
Sodium (Na+) moves passively into the cell across the apical membrane and is actively transported out of the cell across the basolateral membrane via Na+/K+-ATPases.
Reabsorption of many substances is coupled to Na+ reabsorption.
Cotransport: substances move uphill into the cell as Na+ moves downhill via the same cotransporter. This is how glucose, amino acids, and other organic substances are reabsorbed.
Transport Maximum (Tm): mediated-transport-reabsorptive systems have a limit to the amount of material they can transport per unit time.
Glucose: reabsorption is limited by Tm. When plasma glucose exceeds the threshold, glucose starts to appear in urine (glucosuria).
Hyperglycemia: high filtered load of glucose can lead to glucosuria and diabetic nephropathy.

Tubular Secretion

Tubular secretion moves substances from peritubular capillaries into the tubular lumen.
Important secreted substances: H+, K+, organic anions, and foreign chemicals.
Active secretion: requires active transport from the blood side into the tubule cell or from the cell into the lumen.
Secretion increases the ability of the kidneys to dispose of substances.

Metabolism by the Tubules

Renal tubules synthesize glucose during fasting and can catabolize certain organic substances.

Regulation of Membrane Channels and Transporters

Activity or concentrations of the membrane channel and transporter proteins involved in reabsorption or secretion are physiologically controlled.
This regulation is achieved by hormones and paracrine or autocrine factors.

Small Intestine Anatomy

The small intestine has a complex structure that maximizes surface area for digestion and absorption.
Circular folds: surface area specializations of the mucosa and submucosa.
Villi: fingerlike projections covering the circular folds.
Microvilli (brush border): small projections on the surface membranes of epithelial cells covering each villus.
Goblet cells: secrete mucus to lubricate and protect the intestinal wall.
Lacteal: a single, blind-ended lymphatic vessel in the center of each villus.
Capillary network: also present in the center of each villus.

Small Intestine Segments

Duodenum: initial, short segment.
Jejunum: intermediate segment.
Ileum: longest segment.

Small Intestine Secretion

Secretions: approximately 1500 mL of fluid secreted daily from the blood into the lumen.
Mineral ions: Na+, Cl−, and HCO 3 − are secreted into the lumen, followed by water by osmosis.
Osmotic gradient: enhanced by the hypertonic chyme entering from the stomach.
Secretions lubricate the intestinal surface and protect epithelial cells.

Pancreatic Secretions

Exocrine pancreas: secretes HCO 3 − and digestive enzymes into the duodenum.
Acinar cells: secrete enzymes.
Pancreatic duct cells: secrete HCO 3 − to neutralize the acidity of chyme.
CFTR: cystic fibrosis transmembrane conductance regulator, involved in chloride recycling and water movement into the duct lumen.
Zymogens: inactive forms of proteolytic enzymes secreted by the pancreas.

Liver Secretion

Liver: secretes bile into the duodenum.
Gallbladder: stores bile between meals.
Sphincter of Oddi: controls bile flow into the duodenum.

Pancreas

The pancreas has both endocrine and exocrine functions
The exocrine pancreas secretes digestive enzymes and bicarbonate, while the endocrine pancreas secretes hormones like insulin and glucagon
Acinar cells in the pancreas secrete digestive enzymes
Duct cells in the pancreas secrete bicarbonate
The pancreatic duct system connects the pancreas to the duodenum, allowing for the delivery of digestive secretions

Pancreatic Enzyme Secretion

Pancreatic enzymes are secreted in inactive forms, such as trypsinogen, chymotrypsinogen, and procarboxypeptidase
Trypsinogen is activated by enteropeptidase, a brush border enzyme found in the small intestine
Once activated, trypsin activates other pancreatic enzymes
Pancreatic enzyme secretion is stimulated by hormones like cholecystokinin (CCK) and secretin

Bile

Bile is produced by the liver
Bile contains bile salts, cholesterol, phospholipids, bicarbonate, and bile pigments
Bile salts are crucial for fat digestion and absorption
The liver synthesizes and secretes bile salts
Bile is concentrated and stored in the gallbladder

Bile Secretion

Bile secretion is stimulated by secretin
Bile salts are absorbed in the ileum and recycled via the enterohepatic circulation
The liver also secretes cholesterol into bile

Gallbladder

The gallbladder stores and concentrates bile
Contraction of the gallbladder is stimulated by CCK
The sphincter of Oddi controls the flow of bile into the duodenum

Carbohydrate Digestion

Salivary amylase begins carbohydrate digestion in the mouth, but pancreatic amylase is the primary enzyme in the small intestine
Pancreatic amylase breaks down starch into maltose and short glucose chains
Brush border enzymes, such as lactase, sucrase, and maltase, further break down disaccharides into monosaccharides (glucose, fructose, galactose)
Monosaccharides are then absorbed into the bloodstream through the small intestine

Protein Digestion

Pepsin begins protein digestion in the stomach
Pancreatic proteases, including trypsin and chymotrypsin, continue protein breakdown in the small intestine
Brush border enzymes like aminopeptidases and carboxypeptidases help break down peptides into amino acids
Most amino acids are absorbed by secondary active transport

Fat Digestion

Fat digestion mainly occurs in the small intestine
Pancreatic lipase breaks down triglycerides into monoglycerides and free fatty acids
Bile salts solubilize fats, forming micelles for easier absorption
Micelles facilitate the absorption of fatty acids and monoglycerides
Lipid absorption involves the formation of chylomicrons, which enter the lymphatic system and eventually the bloodstream### Protein Digestion and Absorption
Protein digestion begins in the stomach with the help of pepsin, a protease enzyme.
In the small intestine, pancreatic proteases, like trypsin and chymotrypsin, further break down proteins into smaller peptides and amino acids.
Amino acids are absorbed into the intestinal epithelial cells through cotransport with Na+ across the apical membrane.
Amino acids then cross the basolateral membrane by facilitated diffusion using specific transporters.
Once in the interstitial fluid, amino acids diffuse into the blood through capillary pores.
Na+/K+-ATPase pumps on the basolateral membrane provide energy for the whole process.

Fat Digestion and Absorption

Fats are insoluble in water and form large droplets in the stomach.
Pancreatic lipase, a water-soluble enzyme, digests fats only at the surface of droplets, making digestion slow due to a low surface-area-to-volume ratio.
Emulsification process breaks down large fat droplets into smaller ones, greatly increasing the surface area for lipase action. This is achieved by mechanical mixing and the presence of emulsifying agents such as phospholipids from food and bile salts from the liver.
Phospholipids and bile salts are amphipathic, meaning they have both polar and nonpolar parts. Their nonpolar parts interact with the lipid droplets, while the polar parts face the watery environment, preventing reaggregation of droplets.
Colipase, a protein secreted by the pancreas, binds lipase to the surface of lipid droplets, further enhancing digestion.
Bile salts also form micelles, tiny aggregates of bile salts, fatty acids, monoglycerides, and phospholipids. Micelles keep fat digestion products in solution, allowing continued digestion and absorption.
Fatty acids and monoglycerides diffuse across the apical plasma membrane into intestinal epithelial cells.
Inside the cells, fatty acids and monoglycerides are resynthesized into triglycerides in the smooth endoplasmic reticulum, which maintains a gradient favoring absorption from the lumen.
Newly formed triglycerides aggregate into droplets covered by amphipathic proteins and are packaged into chylomicrons, which exit the cell by exocytosis into the interstitial fluid.
Chylomicrons, being too large to enter blood capillaries, enter the lacteals, lymphatic vessels in the intestinal villi.
Chylomicrons travel through the lymphatic system and eventually reach the bloodstream, delivering lipids and fat-soluble vitamins to body cells.

Vitamin Absorption

Fat-soluble vitamins (A, D, E, and K) are solubilized in micelles and follow the pathway for fat absorption.
Water-soluble vitamins are absorbed by diffusion or mediated transport, except vitamin B12.
Vitamin B12, a large charged molecule, requires intrinsic factor, secreted by parietal cells in the stomach, for absorption.
Intrinsic factor-bound vitamin B12 binds to specific sites in the lower ileum, where it is absorbed by endocytosis.

Water and Mineral Absorption

Approximately 80% of the ingested and secreted water (around 8000 mL) is absorbed in the small intestine.
The small intestine is highly permeable to water, and net water diffusion occurs due to the active absorption of solutes.
Na+ is the primary actively transported solute, driven by Na+/K+-ATPase pumps.
Cl- and HCO3- are absorbed with Na+, further contributing to the osmotic gradient for water absorption.
Other minerals, such as K+, Mg2+, PO43-, and Ca2+, are also absorbed along with trace elements like Fe, Zn, and I.

Iron Absorption

Iron is essential for hemoglobin and many enzymes.
About 10% of ingested iron is absorbed each day.
Iron ions are actively transported into intestinal epithelial cells, where most bind to ferritin, an intracellular iron storage protein.
Unbound iron is released into the blood, binding to transferrin, a plasma protein.
Iron absorption is regulated by body iron stores. High iron levels lead to increased ferritin synthesis, reducing iron release into the blood. Conversely, low iron stores reduce ferritin production, increasing iron release.
Excess iron intake can overwhelm homeostatic mechanisms, leading to hemochromatosis, a condition with toxic effects.
Iron absorption is influenced by food types. For example, iron in liver is more readily absorbed than iron in egg yolk, due to phosphate binding in egg yolk.

Nutrient Transport Pathways

Fats and fat-soluble nutrients enter the lymphatic system through lacteals.
All other absorbed nutrients enter the bloodstream through capillaries.
Venous drainage from the intestines, pancreas, and parts of the stomach passes through the hepatic portal vein into the liver before entering the general circulation. This allows the liver to process nutrients before they reach other body organs.
This portal system also carries pancreatic hormones insulin and glucagon to the liver for regulating nutrient metabolism.

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