Study Guide Notes - Urinary System, Fluid Balance, and Digestive System

Urinary System and Fluid Balance

Definitions

• Renal Corpuscle: The initial blood-filtering component of a nephron. It consists of the glomerulus and Bowman's capsule.

• Glomerulus: A network of capillaries within the Bowman's capsule of the kidney. It is responsible for the filtration of blood.

• Proximal Tubules: The section of the nephron immediately following the Bowman's capsule, responsible for the reabsorption of water, ions, and nutrients from the filtrate.

• Osmoreceptors: Sensory receptors that detect changes in osmotic pressure and trigger the release of hormones like ADH to regulate fluid balance.

• Juxtaglomerular Cells: Cells in the kidney that synthesize, store, and secrete renin. They are located in the walls of the afferent arterioles.

• ACE Inhibitors: Medications that block the action of angiotensin-converting enzyme (ACE), leading to vasodilation and reduced blood pressure.

• Hyperkalemia: A condition characterized by an abnormally high concentration of potassium in the blood.

• Renin: An enzyme secreted by the kidney that participates in the renin-angiotensin-aldosterone system (RAAS), regulating blood pressure and fluid balance.

Short Descriptions

• Functions of the Kidneys:

  • Filtration of blood and removal of waste products.

  • Regulation of blood pressure.

  • Regulation of electrolyte balance.

  • Regulation of red blood cell production (via erythropoietin).

  • Regulation of acid-base balance.

• Blood Circulation Through the Kidney:

  • Renal artery → Afferent arterioles → Glomerulus → Efferent arterioles → Peritubular capillaries and Vasa Recta → Renal vein.

• Filtration, Reabsorption, Secretion, and Excretion:

  • Filtration: Movement of fluid and solutes from the glomerulus into Bowman's capsule.

  • Reabsorption: Movement of substances from the renal tubules back into the blood.

  • Secretion: Movement of substances from the blood into the renal tubules.

  • Excretion: Elimination of waste products from the body in the form of urine.

• Glomerular Filtration Pressure (GFP), GFR, and its Controlling Factors:

  • GFP: The net pressure driving fluid from the glomerulus into Bowman's capsule. It's determined by the balance of glomerular hydrostatic pressure, capsular hydrostatic pressure, and blood colloid osmotic pressure.

  • GFR: The glomerular filtration rate, is the volume of fluid filtered from the glomerular capillaries into the Bowman's capsule per unit time. Normal GFR is approximately 125 ml/min.

  • Controlling Factors: Blood pressure, afferent and efferent arteriolar resistance, and plasma protein concentration.

• Production and Functions of ADH, Aldosterone, and Angiotensin II:

  • ADH (Antidiuretic Hormone): Produced by the hypothalamus and released by the posterior pituitary gland. It increases water reabsorption in the kidneys, reducing urine volume.

  • Aldosterone: Produced by the adrenal cortex. It increases sodium reabsorption and potassium secretion in the kidneys, leading to increased water retention and blood pressure.

  • Angiotensin II: Formed as part of the RAAS. It causes vasoconstriction, stimulates aldosterone release, and increases thirst and ADH secretion, all of which increase blood pressure.

• RAAS (Renin-Angiotensin-Aldosterone System):

  • Trigger: Low blood pressure or low sodium levels in the distal convoluted tubule.

  • Mechanism: Renin converts angiotensinogen to angiotensin I, which is then converted to angiotensin II by ACE. Angiotensin II stimulates aldosterone release, vasoconstriction, and ADH secretion, leading to increased blood pressure and sodium retention.

• Functions of Angiotensin II:

  • Vasoconstriction: Increases blood pressure directly.

  • Aldosterone Release: Increases sodium and water reabsorption.

  • ADH Secretion: Increases water reabsorption.

  • Thirst Stimulation: Increases fluid intake.

• pH Changes:

  • Hyperventilation: Leads to respiratory alkalosis (increased pH) due to excessive exhalation of CO_2.

  • Prolonged Vomiting: Leads to metabolic alkalosis (increased pH) due to loss of stomach acid (HCl).

  • Emphysema: Can lead to respiratory acidosis (decreased pH) due to impaired gas exchange and CO_2 retention.

Digestive System

Definitions

• Chemical Digestion: The breakdown of food molecules into smaller molecules by enzymes.

• Myenteric Plexus: A network of nerves located between the longitudinal and circular muscle layers of the digestive tract. It controls gastrointestinal motility.

• Swallowing Reflex: A complex reflex initiated when food is forced into the pharynx. It involves coordinated muscle contractions that propel food into the esophagus while preventing it from entering the trachea.

• GALT (Gut-Associated Lymphoid Tissue): Immune tissue located in the digestive tract that protects the body from pathogens and maintains a healthy gut microbiome.

Descriptions

• Layers of the Digestive System:

  • Mucosa: The innermost layer, composed of epithelium, lamina propria, and muscularis mucosae.

  • Submucosa: Connective tissue layer containing blood vessels, lymph vessels, and nerves.

  • Muscularis Externa: Typically composed of two layers of smooth muscle: an inner circular layer and an outer longitudinal layer. Responsible for peristalsis and segmentation.

  • Serosa/Adventitia: The outermost layer; serosa if within the peritoneal cavity, adventitia if outside.

• Functions:

  • Large Intestine:

    • Absorbs water and electrolytes from undigested material.

    • Forms and stores feces.

    • Harbors gut microbiota.

  • Small Intestine:

    • Primary site of nutrient digestion and absorption.

    • Receives digestive enzymes from the pancreas and bile from the liver.

  • Stomach:

    • Stores food.

    • Mixes food with gastric secretions to form chyme.

    • Begins protein digestion.

    • Regulates the rate at which chyme enters the small intestine.

• Stomach Cells and Their Functions:

  • Mucous Cells: Secrete mucus to protect the stomach lining from acid and enzymes.

  • Parietal Cells: Secrete hydrochloric acid (HCl) and intrinsic factor (necessary for vitamin B12 absorption).

  • Chief Cells: Secrete pepsinogen, an inactive precursor of pepsin, which digests proteins.

  • G Cells: Secrete gastrin, a hormone that stimulates HCl secretion and gastric motility.

• Digestive Enzymes and Their Major Functions:

  • Amylase: Digests carbohydrates. Source: Salivary glands, pancreas. Converts starch to smaller sugars like maltose.

  • Lipase: Digests fats (lipids). Source: Pancreas. Breaks down triglycerides into fatty acids and glycerol.

  • Pepsin: Digests proteins. Source: Stomach (chief cells; secreted as pepsinogen and activated by HCl). Breaks down proteins into smaller peptides.

  • Trypsin: Digests proteins. Source: Pancreas (secreted as trypsinogen and activated in the small intestine). Breaks down proteins into smaller peptides.

• Fat Absorption:

  • Emulsification: Bile salts emulsify large fat globules into smaller droplets.

  • Digestion: Lipase breaks down triglycerides into monoglycerides and fatty acids.

  • Micelle Formation: Monoglycerides and fatty acids associate with bile salts to form micelles.

  • Absorption: Micelles transport lipids to the intestinal cells, where they are absorbed.

  • Chylomicron Formation: Inside the intestinal cells, triglycerides are resynthesized and packaged into chylomicrons.

  • Transport: Chylomicrons enter the lymphatic system and eventually the bloodstream.

Urinary System and Fluid Balance

Definitions

• Renal Corpuscle: The initial blood-filtering component of a nephron. It consists of the glomerulus and Bowman's capsule. Blood plasma is filtered here, initiating urine formation. The structure includes:

  • Glomerulus: A network of capillaries within the Bowman's capsule of the kidney. These capillaries are unique because they are positioned between two arterioles (afferent and efferent), allowing for the regulation of pressure and filtration rate. The glomerulus filters water, ions, glucose, amino acids, and waste products from the blood, forming the glomerular filtrate, which then enters the proximal tubules.

  • Bowman's Capsule: A cup-like sac at the beginning of the nephron that receives the glomerular filtrate.

• Proximal Tubules: The section of the nephron immediately following the Bowman's capsule, responsible for the reabsorption of approximately 65% of water, sodium, glucose, amino acids, and other essential solutes from the filtrate back into the bloodstream. The cells lining the proximal tubules have microvilli to increase the surface area for reabsorption, enhancing their capacity to reclaim vital substances.

• Osmoreceptors: Sensory receptors located in the hypothalamus that detect changes in osmotic pressure (the concentration of solutes) in the blood. When osmotic pressure increases (indicating dehydration), osmoreceptors trigger the release of ADH to promote water reabsorption in the kidneys, reducing urine volume and conserving water.

• Juxtaglomerular Cells: Specialized cells located in the walls of the afferent arterioles of the kidney. These cells synthesize, store, and secrete renin in response to decreased blood pressure, decreased sodium levels, or sympathetic nervous system stimulation. Renin initiates the renin-angiotensin-aldosterone system (RAAS), which plays a crucial role in regulating blood pressure and fluid balance.

• ACE Inhibitors: Medications that block the action of angiotensin-converting enzyme (ACE), which is responsible for converting angiotensin I to angiotensin II. By inhibiting ACE, these drugs reduce the production of angiotensin II, leading to vasodilation (widening of blood vessels) and reduced blood pressure. They are commonly used to treat hypertension and heart failure.

• Hyperkalemia: A condition characterized by an abnormally high concentration of potassium in the blood (typically above 5.5 mEq/L). Hyperkalemia can cause serious cardiac arrhythmias and muscle weakness. It is often caused by kidney dysfunction, certain medications, or excessive potassium intake.

• Renin: An enzyme secreted by the juxtaglomerular cells of the kidney in response to decreased blood pressure, decreased sodium levels, or sympathetic nervous system stimulation. Renin initiates the renin-angiotensin-aldosterone system (RAAS), converting angiotensinogen to angiotensin I. This is the first step in a cascade that leads to increased blood pressure and sodium retention.

Short Descriptions

• Functions of the Kidneys:

  • Filtration of blood and removal of waste products: The kidneys filter approximately 120-150 quarts of blood daily, removing waste products such as urea, creatinine, and excess ions. This filtration process occurs in the glomeruli, where blood is filtered under pressure into Bowman's capsule.

  • Regulation of blood pressure: The kidneys regulate blood pressure through the renin-angiotensin-aldosterone system (RAAS). When blood pressure drops, the kidneys release renin, which initiates a cascade of reactions leading to the production of angiotensin II. Angiotensin II causes vasoconstriction and stimulates the release of aldosterone, both of which increase blood pressure. The kidneys also regulate blood volume, which directly impacts blood pressure.

  • Regulation of electrolyte balance: The kidneys maintain electrolyte balance by regulating the levels of ions such as sodium, potassium, calcium, and phosphate in the blood. They reabsorb electrolytes as needed and excrete excesses in the urine. Aldosterone plays a key role in sodium and potassium balance, while parathyroid hormone (PTH) influences calcium and phosphate balance.

  • Regulation of red blood cell production (via erythropoietin): When the kidneys detect low oxygen levels in the blood, they release erythropoietin (EPO). EPO stimulates the bone marrow to produce more red blood cells, increasing the oxygen-carrying capacity of the blood. This process is essential for preventing and correcting anemia.

  • Regulation of acid-base balance: The kidneys help maintain acid-base balance by excreting hydrogen ions (H^+) and reabsorbing bicarbonate (HCO_3^-). They can generate new bicarbonate ions to replenish those lost in buffering acids. This regulation is critical for maintaining a stable pH in the blood, which is essential for normal cell function.

• Blood Circulation Through the Kidney:

  • Renal artery → Afferent arterioles → Glomerulus → Efferent arterioles → Peritubular capillaries and Vasa Recta → Renal vein.

    • Renal Artery: The main artery supplying blood to the kidney. It branches off the abdominal aorta and enters the kidney at the hilum.

    • Afferent Arterioles: Small blood vessels that branch off the renal artery and lead into the glomerulus. These arterioles carry blood to the glomerulus for filtration.

    • Glomerulus: A network of capillaries where filtration of blood occurs. It filters water, ions, glucose, amino acids, and waste products from the blood.

    • Efferent Arterioles: Small blood vessels that carry blood away from the glomerulus. These arterioles are narrower than the afferent arterioles, which helps to increase the pressure within the glomerulus.

    • Peritubular Capillaries: A network of capillaries that surround the renal tubules. These capillaries are involved in the reabsorption of water and solutes from the filtrate back into the bloodstream, as well as the secretion of certain substances from the blood into the filtrate.

    • Vasa Recta: Specialized peritubular capillaries that follow the loop of Henle in the medulla of the kidney. They play a crucial role in maintaining the concentration gradient in the medulla, which is essential for the production of concentrated urine.

    • Renal Vein: The main vein that carries blood away from the kidney. It drains into the inferior vena cava.

• Filtration, Reabsorption, Secretion, and Excretion:

  • Filtration: Movement of fluid and solutes from the glomerulus into Bowman's capsule. This process is driven by the pressure gradient between the glomerulus and Bowman's capsule. The glomerular filtration membrane allows small molecules to pass through while preventing larger molecules, such as proteins and blood cells, from entering the filtrate.

  • Reabsorption: Movement of substances from the renal tubules back into the blood. This process occurs in the proximal tubules, loop of Henle, distal tubules, and collecting ducts. Reabsorption is highly selective and involves both active and passive transport mechanisms. Substances such as glucose, amino acids, sodium, and water are reabsorbed to maintain electrolyte balance and prevent dehydration.

  • Secretion: Movement of substances from the blood into the renal tubules. This process allows the body to eliminate waste products and toxins that were not initially filtered in the glomerulus. Secretion occurs mainly in the proximal and distal tubules and involves active transport mechanisms.

  • Excretion: Elimination of waste products from the body in the form of urine. Urine is collected in the renal pelvis and flows through the ureters to the bladder, where it is stored until it is eliminated through the urethra.

• Glomerular Filtration Pressure (GFP), GFR, and its Controlling Factors:

  • GFP: The net pressure driving fluid from the glomerulus into Bowman's capsule. It's determined by the balance of glomerular hydrostatic pressure, capsular hydrostatic pressure, and blood colloid osmotic pressure.

    • Glomerular hydrostatic pressure: The pressure exerted by the blood within the glomerular capillaries, promoting filtration.

    • Capsular hydrostatic pressure: The pressure exerted by the fluid in Bowman's capsule, opposing filtration.

    • Blood colloid osmotic pressure: The pressure exerted by the proteins in the blood, which tends to pull water back into the capillaries, opposing filtration.

  • GFR: The glomerular filtration rate, is the volume of fluid filtered from the glomerular capillaries into the Bowman's capsule per unit time. Normal GFR is approximately 125 ml/min.

  • Controlling Factors: Blood pressure, afferent and efferent arteriolar resistance, and plasma protein concentration.

    • Blood pressure: Changes in blood pressure directly affect GFR. Increased blood pressure increases GFR, while decreased blood pressure decreases GFR.

    • Afferent and efferent arteriolar resistance: Constriction of the afferent arteriole decreases GFR, while constriction of the efferent arteriole increases GFR (up to a certain point). Dilation of the afferent arteriole increases GFR, while dilation of the efferent arteriole decreases GFR.

    • Plasma protein concentration: Changes in plasma protein concentration affect the blood colloid osmotic pressure, which in turn affects GFR. Increased plasma protein concentration decreases GFR, while decreased plasma protein concentration increases GFR.

• Production and Functions of ADH, Aldosterone, and Angiotensin II:

  • ADH (Antidiuretic Hormone): Produced by the hypothalamus and released by the posterior pituitary gland. It increases water reabsorption in the kidneys, reducing urine volume.

    • Production: Synthesized in the hypothalamus by neurons in the supraoptic and paraventricular nuclei.

    • Release: Transported to the posterior pituitary gland, where it is stored and released in response to increased blood osmolarity or decreased blood volume.

    • Functions: ADH acts on the collecting ducts of the kidneys, increasing their permeability to water. This allows more water to be reabsorbed from the filtrate back into the bloodstream, reducing urine volume and concentrating the urine.

  • Aldosterone: Produced by the adrenal cortex. It increases sodium reabsorption and potassium secretion in the kidneys, leading to increased water retention and blood pressure.

    • Production: Synthesized in the adrenal cortex in response to angiotensin II or increased potassium levels.

    • Functions: Aldosterone acts on the distal tubules and collecting ducts of the kidneys, increasing the reabsorption of sodium and the secretion of potassium. Since water follows sodium, this leads to increased water retention, increased blood volume, and increased blood pressure.

  • Angiotensin II: Formed as part of the RAAS. It causes vasoconstriction, stimulates aldosterone release, and increases thirst and ADH secretion, all of which increase blood pressure.

    • Production: Formed from angiotensin I by the action of angiotensin-converting enzyme (ACE), which is primarily located in the lungs.

    • Functions: Angiotensin II is a potent vasoconstrictor, causing blood vessels to narrow and blood pressure to increase. It also stimulates the release of aldosterone from the adrenal cortex, leading to increased sodium and water reabsorption in the kidneys. Additionally, it stimulates thirst and the release of ADH, further increasing blood volume and blood pressure.

• RAAS (Renin-Angiotensin-Aldosterone System):

  • Trigger: Low blood pressure or low sodium levels in the distal convoluted tubule.

  • Mechanism: Renin converts angiotensinogen to angiotensin I, which is then converted to angiotensin II by ACE. Angiotensin II stimulates aldosterone release, vasoconstriction, and ADH secretion, leading to increased blood pressure and sodium retention.

    • Renin Release: Juxtaglomerular cells in the kidney release renin in response to:

      • Decreased blood pressure in the afferent arteriole.

      • Decreased sodium levels in the distal convoluted tubule (detected by the macula densa).

      • Sympathetic nervous system stimulation.

    • Angiotensinogen Conversion: Renin converts angiotensinogen (a protein produced by the liver) into angiotensin I.

    • ACE Conversion: Angiotensin-converting enzyme (ACE), primarily located in the lungs, converts angiotensin I into angiotensin II.

    • Effects of Angiotensin II: Angiotensin II has multiple effects that increase blood pressure and sodium retention:

      • Vasoconstriction: Constricts blood vessels, increasing blood pressure directly.

      • Aldosterone Release: Stimulates the adrenal cortex to release aldosterone, increasing sodium reabsorption in the kidneys.

      • ADH Secretion: Stimulates the posterior pituitary gland to release ADH, increasing water reabsorption in the kidneys.

      • Thirst Stimulation: Stimulates the thirst center in the brain, increasing fluid intake.

• Functions of Angiotensin II:

  • Vasoconstriction: Increases blood pressure directly.

  • Aldosterone Release: Increases sodium and water reabsorption.

  • ADH Secretion: Increases water reabsorption.

  • Thirst Stimulation: Increases fluid intake.

• pH Changes:

  • Hyperventilation: Leads to respiratory alkalosis (increased pH) due to excessive exhalation of CO_2.

    • Mechanism: Hyperventilation increases the rate of carbon dioxide removal from the body.

    • Effect on pH: This leads to a decrease in the partial pressure of carbon dioxide (PCO2) in the blood, which reduces the concentration of carbonic acid (H2CO3). The decrease in acid shifts the bicarbonate buffer system (H2O + CO2 \rightleftharpoons H2CO3 \rightleftharpoons H^+ + HCO3^-) to the left, consuming hydrogen ions and increasing the blood pH.

  • Prolonged Vomiting: Leads to metabolic alkalosis (increased pH) due to loss of stomach acid (HCl).

    • Mechanism: Prolonged vomiting results in the loss of hydrochloric acid (HCl) from the stomach.

    • Effect on pH: This loss of acid directly reduces the hydrogen ion concentration in the body, leading to an increase in blood pH. The kidneys attempt to compensate by retaining hydrogen ions and excreting bicarbonate ions, but prolonged vomiting can overwhelm these compensatory mechanisms.

  • Emphysema: Can lead to respiratory acidosis (decreased pH) due to impaired gas exchange and CO_2 retention.

    • Mechanism: Emphysema damages the alveoli in the lungs, reducing the surface area available for gas exchange. This impairs the elimination of carbon dioxide from the body.

    • Effect on pH: The retained carbon dioxide increases the partial pressure of carbon dioxide (PCO2) in the blood, leading to an increase in carbonic acid (H2CO_3) concentration. The increase in acid shifts the bicarbonate buffer system to the right, increasing hydrogen ion concentration and decreasing blood pH.

Digestive System

Definitions

• Chemical Digestion: The breakdown of food molecules into smaller molecules by enzymes. This process begins in the mouth with salivary amylase breaking down carbohydrates, continues in the stomach with pepsin breaking down proteins, and is completed in the small intestine with enzymes from the pancreas and intestinal cells breaking down carbohydrates, proteins, and fats.

• Myenteric Plexus: A network of nerves located between the longitudinal and circular muscle layers of the digestive tract. It controls gastrointestinal motility, including peristalsis and segmentation. Also known as Auerbach's plexus, it is a major component of the enteric nervous system.

• Swallowing Reflex: A complex reflex initiated when food is forced into the pharynx. It involves coordinated muscle contractions that propel food into the esophagus while preventing it from entering the trachea. The swallowing center in the brainstem coordinates the actions of the muscles in the mouth, pharynx, and esophagus to ensure that food is safely and efficiently moved into the stomach.

• GALT (Gut-Associated Lymphoid Tissue): Immune tissue located in the digestive tract that protects the body from pathogens and maintains a healthy gut microbiome. GALT includes Peyer's patches in the small intestine, lymphoid follicles in the large intestine, and immune cells scattered throughout the digestive tract.

Descriptions

• Layers of the Digestive System:

  • Mucosa: The innermost layer, composed of epithelium, lamina propria, and muscularis mucosae.

    • Epithelium: The type of epithelium varies along the digestive tract, depending on the function of the region. It can be simple columnar (in the stomach and intestines) for secretion and absorption or stratified squamous (in the esophagus) for protection.

    • Lamina Propria: A layer of loose connective tissue that contains blood vessels, lymphatic vessels, and immune cells. It supports the epithelium and provides nutrients and immune protection.

    • Muscularis Mucosae: A thin layer of smooth muscle that creates local movements of the mucosa, enhancing its contact with the contents of the lumen.

  • Submucosa: Connective tissue layer containing blood vessels, lymph vessels, and nerves. It provides support and elasticity to the digestive tract. The submucosa also contains the submucosal plexus (Meissner's plexus), which regulates local blood flow, secretion, and absorption.

  • Muscularis Externa: Typically composed of two layers of smooth muscle: an inner circular layer and an outer longitudinal layer. Responsible for peristalsis and segmentation. In some regions, such as the stomach, there may be an additional oblique layer.

  • Serosa/Adventitia: The outermost layer; serosa if within the peritoneal cavity, adventitia if outside. The serosa is a serous membrane that secretes a watery fluid to lubricate the digestive tract and reduce friction. The adventitia is a fibrous connective tissue layer that anchors the digestive tract to surrounding structures.

• Functions:

  • Large Intestine:

    • Absorbs water and electrolytes from undigested material.

    • Forms and stores feces.

    • Harbors gut microbiota: The large intestine contains a diverse community of bacteria, archaea, fungi, and viruses, collectively known as the gut microbiota. These microorganisms play important roles in:

      • Fermenting undigested carbohydrates.

      • Synthesizing vitamins (such as vitamin K and B vitamins).

      • Training the immune system.

      • Protecting against pathogenic bacteria.

  • Small Intestine:

    • Primary site of nutrient digestion and absorption.

    • Receives digestive enzymes from the pancreas and bile from the liver.

  • Stomach:

    • Stores food.

    • Mixes food with gastric secretions to form chyme.

    • Begins protein digestion.

    • Regulates the rate at which chyme enters the small intestine.

• Stomach Cells and Their Functions:

  • Mucous Cells: Secrete mucus to protect the stomach lining from acid and enzymes. The mucus forms a protective barrier that prevents the stomach from digesting itself.

  • Parietal Cells: Secrete hydrochloric acid (HCl) and intrinsic factor (necessary for vitamin B12 absorption). HCl helps to denature proteins and activate pepsinogen, while intrinsic factor is essential for the absorption of vitamin B12 in the ileum.

  • Chief Cells: Secrete pepsinogen, an inactive precursor of pepsin, which digests proteins. Pepsinogen is activated by HCl in the stomach lumen to form pepsin.

  • G Cells: Secrete gastrin, a hormone that stimulates HCl secretion and gastric motility. Gastrin also promotes the growth of the gastric mucosa.

• Digestive Enzymes and Their Major Functions:

  • Amylase: Digests carbohydrates. Source: Salivary glands, pancreas. Converts starch to smaller sugars like maltose.

    • Salivary Amylase: Secreted by the salivary glands in the mouth. Initiates the digestion of starch into smaller polysaccharides and maltose.

    • Pancreatic Amylase: Secreted by the pancreas into the small intestine. Continues the digestion of starch into maltose.

  • Lipase: Digests fats (lipids). Source: Pancreas. Breaks down triglycerides into fatty acids and glycerol.

    • Pancreatic Lipase: Secreted by the pancreas into the small intestine. Breaks down triglycerides into monoglycerides and fatty acids with the help of co-lipase.

  • Pepsin: Digests proteins. Source: Stomach (chief cells; secreted as pepsinogen and activated by HCl). Breaks down proteins into smaller peptides.

  • Trypsin: Digests proteins. Source: Pancreas (secreted as trypsinogen and activated in the small intestine). Breaks down proteins into smaller peptides.

• Fat Absorption:

  • Emulsification: Bile salts emulsify large fat globules into smaller droplets. This increases the surface area for lipase to act on.

  • Digestion: Lipase breaks down triglycerides into monoglycerides and fatty acids.

  • Micelle Formation: Monoglycerides and fatty acids associate with bile salts to form micelles. Micelles are small, spherical aggregates that transport lipids to the intestinal cells.

  • Absorption: Micelles transport lipids to the intestinal cells, where they are absorbed. The lipids diffuse across the cell membrane and enter the cytoplasm.

  • Chylomicron Formation: Inside the intestinal cells, triglycerides are resynthesized and packaged into chylomicrons. Chylomicrons are large lipoprotein particles that transport lipids from the intestine to the rest of the body.

  • Transport: Chylomicrons enter the lymphatic system and eventually the bloodstream. They are too large to enter the blood capillaries directly, so they enter the lymphatic capillaries (lacteals) in the villi of the small intestine. From the lymphatic system, they are transported to the thoracic duct and then enter the bloodstream.