Glomerular Filtration Rate (GFR) Regulation Quiz

Regulation Mechanisms of Glomerular Filtration Rate (GFR)

• Myogenic regulation: Vascular smooth muscle contracts when stretched and relaxes when not stretched, preventing glomerular blood pressure from reaching damaging levels.
• Autoregulation: Kidneys adjust their own resistance to maintain a nearly constant GFR despite fluctuations in arterial blood pressure, using myogenic and tubuloglomerular feedback.
• Neural regulation: Norepinephrine released by sympathetic nerve fibers causes vasoconstriction, increasing peripheral resistance and blood pressure, leading to decreased GFR.
• Hormonal regulation: Renin-Angiotensin-Aldosterone mechanism is the main mechanism for increasing blood pressure, involving the release of renin by granular cells and activation of the sympathetic nervous system.
• Tubules I: Water reabsorption in the proximal convoluted tubule (PCT) is obligatory, while in the collecting ducts, aquaporins are inserted based on osmolality levels signaling the release or inhibition of ADH, facilitating facultative water reabsorption.
• Tubules II: Sodium is primarily reabsorbed through transcellular and active transport, involving the Na-K ATPase pump and the role of aldosterone in retaining sodium and potassium channels in the collecting ducts and distal convoluted tubule (DCT).
• Tubules III: Glucose is reabsorbed by secondary active transport and transport maximum is reached when transport proteins are saturated, leading to the excess excretion in urine.
• Endocrine function of the kidneys: Renin is released by the kidneys to raise blood pressure by initiating the renin-angiotensin-aldosterone mechanism, while aldosterone regulates sodium reabsorption and potassium secretion.
• Acid-base balance: Our pH is 7 due to the kidneys' role in regulating the acid-base balance through the excretion of hydrogen ions and reabsorption of bicarbonate ions.

Gastrointestinal Physiology and Pancreatic Functions

• Parietal cells in the stomach produce hydrochloric acid (HCl) and intrinsic factor, facilitated by microvilli providing surface area for secretion
• HCl is crucial for activating pepsin, a protein-digesting enzyme, while intrinsic factor aids in vitamin B12 absorption in the small intestine
• Gastric secretion is regulated by both neural (vagus and sympathetic nerves) and hormonal factors (gastrin, ACh, histamine)
• Three phases of gastric secretion: cephalic (before food enters stomach), gastric (when food reaches stomach), and intestinal (stimulatory and inhibitory components)
• The autonomic nervous system, including long (vagus nerve-mediated) and short (local enteric) nerve reflexes, plays a key role in regulating gastric secretion
• The enteric nervous system, an in-house nerve supply of the alimentary canal, has both short and long reflex arcs and communicates widely to regulate digestive system activity
• The pancreas contains exocrine glands that produce digestive enzymes (proteases, amylase, lipase) and bicarbonate critical to proper digestion
• Pancreatic juices, released into the duodenum, assist in the digestion of fats, carbohydrates, and proteins
• The pancreas also produces bile, which is released into the duodenum and aids in digestion
• Acinar cells are the exocrine cells of the pancreas responsible for producing and transporting enzymes into the duodenum
• Pancreatic juice consists of digestive enzymes (proteases) and bicarbonate, essential for reducing digestible macromolecules into forms capable of absorption
• Trypsinogen, a major pancreatic protease, is activated by enterokinase in the intestinal mucosa to digest proteins

Defecation Reflexes and Anatomy of Liver and Bile

• Defecation involves two main reflexes: intrinsic myenteric defecation reflex and parasympathetic defecation reflex.
• Intrinsic myenteric defecation reflex is triggered by the distention of the rectal wall, leading to increased peristalsis and relaxation of the internal anal sphincter.
• Parasympathetic defecation reflex works similarly to the intrinsic reflex, but involves parasympathetic nerve fibers and enhances the process.
• Other defecation reflexes include gastrocolic, gastrolienal, enterogastric, and duodenocolic reflexes, each triggered by specific stimuli in the gastrointestinal system.
• The liver, the largest gland in the body, has four lobes and is located in the right hypochondriac and epigastric region, mostly within the ribcage.
• Liver cells, hepatocytes, form liver lobules and are involved in bile secretion, glucose storage, protein synthesis, and detoxification.
• Bile, an alkaline yellow/green fluid, contains bile salts, bile pigments, cholesterol, triglycerides, and phospholipids, with bile salts aiding in the digestive process.
• Bile salts, cholesterol derivatives, are essential for the digestion and absorption of fats and are recycled through the enterohepatic circulation.
• Bilirubin, the chief bile pigment, is a waste product of heme from broken down erythrocytes and is excreted into bile and metabolized by bacteria in the small intestine.
• Protein absorption involves dietary protein and protein from used mucosa, with the process beginning in the stomach and continuing in the small intestine.
• The process of protein absorption includes digestion by stomach acid and enzymes, absorption in the small intestine, and transport to the liver via the hepatic portal system.
• Protein absorption is essential for the body's growth, repair, and maintenance, and any disruptions in the process can lead to malnutrition and health issues.

Anatomy and Function of the Digestive System

• The digestive system consists of the alimentary canal and accessory organs, with the purpose of breaking down food and converting it to energy.
• Essential activities of the digestive system include ingestion, propulsion, mechanical breakdown, digestion, absorption, and defecation.
• The mouth and accessory organs are involved in ingestion, propulsion, breakdown, and digestion through processes like chewing and salivary amylase secretion.
• The pharynx and esophagus mainly aid in propulsion through peristalsis.
• The stomach contributes to mechanical breakdown, protein digestion, and minimal absorption, with the production of pepsin and hydrochloric acid.
• The small intestines and associated organs facilitate breakdown, digestion, and absorption of various nutrients, including carbs, protein, fat, and nucleic acid.
• The large intestine is involved in the digestion of remaining food by enteric bacteria, absorption of water and electrolytes, propulsion of feces, and defecation.
• The abdominal anatomy includes the peritoneum, mesentery, and omentum, which provide structural support and routes for blood vessels, lymphatics, and nerves.
• The blood supply to the intestines comes from the splanchnic circulation, including the celiac artery, superior mesenteric arteries, and inferior mesenteric arteries.
• The hepatic portal circulation collects nutrient-rich venous blood from the digestive viscera and delivers it to the liver.
• Digestion is the process of breaking down food by mechanical and enzymatic action in the alimentary canal into substances that can be used by the body.
• Digestive steps in the mouth include ingestion, mechanical breakdown through chewing, initiation of propulsion by swallowing, and the start of polysaccharide digestion, while the stomach continues mechanical breakdown and protein digestion, primarily through pepsin and hydrochloric acid.