RAT 15: BMSP 2136: Renal Filtration and Digestive System Module Study Guide
Glomerular Filtration: The Filtration Membrane and Filtrate
The separation between blood in the glomerulus and the capsular space is maintained by three distinct barriers: - 1. Fenestrated glomerular capillary endothelial cells: The glomerulus is a type of fenestrated capillary, characterized by pores that permit the passage of large volumes of fluids and solutes. - 2. Basal lamina. - 3. Podocytes: These form the visceral layer of the glomerular capsule.
Permeability Constraints of the Capillary: - Permitted items: Large volumes of fluids and solutes. - Prohibited items: Blood cells and platelets.
The Glomerular Filtration Rate (GFR) and Pressures
Glomerular Filtration Rate (GFR): Defined as the rate at which filtrate is produced within the glomeruli of the kidneys.
Daily Filtrate Production: Approximately liters.
Hydrostatic Pressure (HP): The force exerted by a fluid against the wall of its container. In the context of blood vessels, it is equal to blood pressure and serves to push water out of the capillary.
Colloid Osmotic Pressure (COP): Pressure generated by proteins (specifically albumin) within the plasma. This force pulls water into the capillaries via osmosis.
Net Filtration Pressure (NFP): This determines the net direction of water movement between capillaries and interstitial fluid. - If HP > COP, water moves out of the capillary. - If HP < COP, water moves into the capillary.
Net Filtration Pressure at the Glomerulus
Glomerular Hydrostatic Pressure (GHP): - Represents the blood pressure within the glomerulus. - This force causes blood/fluid to leave the glomerulus. - It is higher than typical systemic capillary pressure because blood enters a high-resistance efferent arteriole, which has a small diameter and smooth muscle.
Glomerular Colloid Osmotic Pressure (GCOP): - This force causes water to leave the glomerular blood (moving through the filtration membrane).
Capsular Hydrostatic Pressure (CHP): - This is the hydrostatic pressure within the capsular space. - This force pushes water into the glomerular capillaries (opposing filtration). - It is higher than tissue hydrostatic pressure in systemic capillaries due to the small diameter of the renal tube.
Glomerular Net Filtration Pressure (NFP): - This is the combined force of GHP, GCOP, and CHP. - Calculation: . - Standard Value: Measures approximately . This pressure drives fluid out of the glomerulus. - Favoring Filtration: GHP drives fluid out. - Opposing Filtration: GCOP and CHP drive fluid into the capillaries.
Comparative Filtration: Glomeruli filter more fluid than systemic capillaries.
Factors Affecting and Regulating the GFR
Pressure Gradients: - A high pressure gradient leads to more filtration. - A low pressure gradient leads to less filtration.
Arteriole Regulation (Analogy): - Afferent Arteriole (The Faucet): - Vasoconstriction: "Turns down" the flow, decreasing GHP and GFR. - Vasodilation: "Turns up" the flow, increasing GHP and GFR. - Glomerulus (The Basin). - Efferent Arteriole (The Drainpipe): - Vasoconstriction: "Clogs" the drain, causing blood to back up. This increases GHP and GFR. - Vasodilation: "Unclogs" the drain, increasing flow out. This decreases GHP and GFR.
Autoregulation: Maintains a relatively constant GFR despite systemic blood pressure changes through local kidney responses. - Myogenic mechanism: Acts to restore GFR by changing vessel diameter. - Tubuloglomerular feedback.
Atrial Natriuretic Peptide (ANP): - Produced in the heart when atrial blood volume increases. - Mechanism: Dilates afferent arterioles and constricts efferent arterioles. - Impact: Raises GHP and GFR, leading to more fluid loss, which decreases blood volume and pressure.
Renin-Angiotensin-Aldosterone System (RAAS): - Primary Function: Maintaining systemic blood pressure. - Renin: An enzyme produced in the kidneys. It catalyzes the conversion of angiotensinogen (produced in the liver) to angiotensin-I (Ang-I). - Angiotensin Converting Enzyme (ACE): Produced in the endothelial cells of the lungs. It catalyzes the conversion of Ang-I to the active form, angiotensin-II (Ang-II). - Effects of Angiotensin-II (Ang-II): - Promotes vasoconstriction of efferent arterioles. - Promotes vasoconstriction of systemic blood vessels. - Promotes reabsorption of sodium () and chloride () ions from the proximal tubule; water follows these ions. - Promotes aldosterone release, increasing reabsorption of sodium ions and water. - Stimulates thirst.
Renal Failure: A condition where kidneys cannot perform vital functions. - Uremia: A buildup of waste products and fluid/electrolyte/acid-base imbalance. Defined as a state where GFR is less than of normal.
Overview of the Digestive System: Blood Supply, Nerve Supply, and Histology
Arterial Supply to Abdominal Organs: - 1. Celiac trunk. - 2. Superior mesenteric artery. - 3. Inferior mesenteric artery.
Venous Drainage: - Hepatic portal vein: Drains digestive organs and delivers blood to the liver for processing. - Hepatic veins: Drain the liver and deliver blood to the inferior vena cava.
Motility: Essential for digestion, nutrient absorption, waste elimination, and regulating hunger/satiety. - Parasympathetic Nervous System (PNS): Increases motility. - Sympathetic Nervous System (SNS): Decreases motility.
Enteric Nervous System (ENS): A self-contained branch of the autonomic nervous system extending from the esophagus to the anus; regulates secretion and motility.
Histology of the Alimentary Canal: - Lumen: The hollow space where food and waste travel. - Mucosa: Comprised of the Epithelium (Simple columnar from stomach to large intestine, rich in mucus-secreting goblet cells), Lamina propria, and Muscularis mucosae. - Submucosa: Contains the submucosal plexus. - Muscularis externa: Contains the myenteric plexus. Typically arranged in two layers: inner circular and outer longitudinal smooth muscle. - Outer Layer: Called serosa if the organ is within the peritoneal cavity; called adventitia if the organ is outside.
The Oral Cavity, Pharynx, and Esophagus
Terminology: - Bolus: A moistened, partially digested ball of food. - Mastication: The mechanical process of chewing, breaking food into smaller particles to aid chemical digestion.
Anatomy of the Mouth: - Buccinator muscles: Form the cheeks; lined with stratified squamous nonkeratinized epithelium. - Labial frenulum: Mucosa attaching lips to gums. - Vestibule: Space between lips/cheeks and teeth/gums. - Palate: The roof of the mouth, divided into the hard palate and soft palate. - Uvula: Extension of the soft palate that seals the nasopharynx during swallowing.
Teeth: - Alveoli: Tooth sockets. - Periodontal ligament: Holds teeth in place. - Crown: Visible portion; coated in enamel (secreted calcium hydroxyapatite crystals). - Root: Embedded in the alveolus; composed of cementum (mineralized bone-like tissue). - Dentin: Inner mineralized material. - Pulp: Soft inner gelatinous substance in the pulp cavity and root canal.
The Tongue: - Lingual frenulum: Prevents excessive posterior movement. - Papillae: Epithelial protrusions; some contain taste buds. - Extrinsic muscles: Move the tongue to help form a bolus. - Intrinsic muscles: Control shape/size to push food against the hard palate.
Salivary Glands: - Parotid: Over the masseter muscle; parotid duct opens near the second molar. - Submandibular: Medial to the mandible body. - Sublingual: Inferior to the tongue. - Secretory cells: Serous cells (water-based enzymes, stimulated by PNS/ACh/smell) and Mucous cells (mucus, stimulated by SNS).
Saliva Components: - Salivary amylase: Catalyzes carbohydrate digestion (polysaccharides to smaller units). - Lysozyme: Kills bacteria by perforating plasma membranes. - Secretory IgA: Mediates pathogen destruction. - Bicarbonate ions: Neutralize regurgitated stomach acid.
The Pharynx: - Divisions: Nasopharynx, Oropharynx, Laryngopharynx. - Alimentary path: Oropharynx and laryngopharynx (lined with stratified squamous epithelium). - Muscles: Pharyngeal constrictor muscles (upper, middle, lower).
The Esophagus: - Located posterior to the trachea; lined with stratified squamous nonkeratinized epithelium. - Sphincters: Upper esophageal sphincter and Gastroesophageal (Lower) esophageal sphincter. - Esophageal hiatus: Opening in the diaphragm for the esophagus and vagus nerves.
Deglutition (Swallowing): - 1. Voluntary phase: Tongue pushes bolus toward the oropharynx. - 2. Pharyngeal phase: Bolus enters oropharynx; soft palate and epiglottis seal off nasopharynx and larynx. - 3. Esophageal phase: Peristaltic waves move bolus to the stomach.
The Stomach
Gross Anatomy: - Regions: Cardia (entry), Fundus (dome top), Body (largest), Pyloric antrum, and Pylorus (terminal end with the pyloric sphincter). - Curvatures: Greater (left convex) and Lesser (right concave). - Rugae: Interior folds allowing for expansion.
Histology: - Muscularis externa has an additional inner oblique layer of smooth muscle. - Chyme: Liquid mixture of bolus and gastric juice. - Gastric pits: Indents in the mucosa leading to gastric glands.
Gastric Gland Cells: - Mucous neck cells: Secrete acidic mucus. - Parietal cells: Secrete Hydrochloric acid (HCl) (activates pepsinogen; creates acidic pH). - Chief cells: Secrete pepsinogen (becomes active pepsin in acid to digest protein). - Enteroendocrine cells (DNES): Secrete gastrin (stimulates acid secretion).
Functions: Secretion, Propulsion, and Digestion. (Absorption is minimal, e.g., alcohol).
The Small Intestine
Processes: Secretion, Digestion, Absorption, and Propulsion.
Enterocytes: Cells producing digestive enzymes, hormones, and mucus.
Divisions: - Duodenum: Initial shortest segment; retroperitoneal; contains major duodenal papilla and Brunner’s glands (alkaline mucus). - Jejunum: Middle portion; most active site for chemical digestion and absorption. - Ileum: Final segment; ends at the ileocecal valve to prevent bacterial backflow from the large intestine.
Surface Area Enhancements: - Circular folds (visible to naked eye). - Villi. - Microvilli: Create the "brush border."
Motility: Includes segmentation (squeezing motion of circular smooth muscle).
The Large Intestine
Functions: Water and electrolyte absorption; secretion (mucus); propulsion; defecation.
Segments: - Cecum. - Colon: Ascending (and hepatic/right colic flexure), Transverse (and splenic/left colic flexure), Descending, and Sigmoid. - Rectum.
Sphincters of the Anus: - Internal anal sphincter: Involuntary; thickened circular smooth muscle. - External anal sphincter: Voluntary; skeletal muscle controlled by the cerebral cortex.
Unique Histology: - Taeniae coli: Three ribbons of longitudinal muscle. - Haustrum: Pockets caused by taeniae coli tension. - Epiploic appendages: Fat-filled pouches on the serosa.
Gut Flora: Beneficial bacteria (~ species) that produce vitamins, metabolize undigested materials, deter pathogens, and stimulate the immune system.
Additional Dynamic Study Module Data
General Values: - Normal GFR: . - Urine production in hours: .
Structures and Systems: - Juxtaglomerular Apparatus (JGA): Secretes renin in response to low BP. - Vasa recta: Acts as a countercurrent exchanger in the renal medulla. - Countercurrent mechanism: Creates a steep concentration gradient for water reabsorption. - Antidiuretic Hormone (ADH): Regulates facultative water reabsorption; distal tubule/collecting ducts are relatively impermeable to water in its absence. - Thick ascending limb: Site where chloride ions are actively reabsorbed. - Bicarbonate ions: Regulated in the proximal tubule to manage blood pH.