Digestive System Physiology

Digestion

Digestion is the process by which food is broken down into smaller, absorbable components. It involves both mechanical and chemical processes.

• Mechanical Digestion: Physical breakdown of food (e.g., chewing, churning in the stomach).

• Chemical Digestion: Enzymatic breakdown of macromolecules into monomers (e.g., proteins to amino acids).

• Chyme: The semi-fluid mass of partly digested food expelled by the stomach into the duodenum.

• Peristaltic Waves: Rhythmic contractions of smooth muscle that propel food through the digestive tract.

Example: Chewing is mechanical digestion, while salivary amylase breaking down starch is chemical digestion.

Role of Dietary Fats

Dietary fats are essential for energy storage, cell membrane structure, and absorption of fat-soluble vitamins.

• Key Point: Fats provide long-term energy and are necessary for hormone production.

• Why Needed: Essential fatty acids cannot be synthesized by the body and must be obtained from the diet.

Metabolism

Metabolism encompasses all chemical reactions in the body, including those that build up (anabolism) and break down (catabolism) molecules.

• Anabolism: Synthesis of complex molecules from simpler ones (e.g., protein synthesis).

• Catabolism: Breakdown of complex molecules into simpler ones (e.g., glycolysis).

Cellular Respiration

Cellular respiration is the process by which cells generate ATP from nutrients. The end goal is to produce energy for cellular activities.

• Three Major Processes:

  1. Glycolysis

  2. Krebs Cycle (Citric Acid Cycle)

  3. Electron Transport Chain

• Equation:

Cholesterol

Cholesterol is a lipid molecule essential for cell membrane structure and hormone synthesis. It is not always harmful; its impact depends on its type and concentration.

• HDL (High-Density Lipoprotein): 'Good' cholesterol, helps remove excess cholesterol from the bloodstream.

• LDL (Low-Density Lipoprotein): 'Bad' cholesterol, can deposit in arteries and increase risk of cardiovascular disease.

Hypoproteinemia

Hypoproteinemia is a condition characterized by abnormally low levels of protein in the blood.

• Key Sign: Edema (swelling due to fluid accumulation).

Acid-Base Disorders

• Metabolic Acidosis: Decreased blood pH due to increased acid or loss of bicarbonate.

• Respiratory Acidosis: Decreased blood pH due to impaired CO2 removal by the lungs.

Diabetes

• Diabetes Mellitus: Chronic condition characterized by high blood glucose due to insulin deficiency or resistance.

• Diabetes Insipidus: Disorder of water balance due to ADH deficiency or insensitivity.

Hepatocytes

Hepatocytes are the main functional cells of the liver, responsible for metabolism, detoxification, and protein synthesis.

Mechanisms of Heat Production

The body produces heat through several mechanisms:

• Basal metabolic rate

• Muscle activity (shivering)

• Hormonal effects (thyroid hormones)

• Brown adipose tissue metabolism

Structure & Function of Digestive and Renal Organs

Mesenteries

Mesenteries are folds of the peritoneum that support and anchor the intestines, providing a pathway for blood vessels and nerves.

Liver

The liver is a vital organ involved in metabolism, detoxification, and production of bile.

Gallbladder

The gallbladder stores and concentrates bile, releasing it into the small intestine to aid fat digestion.

Pancreas

The pancreas produces digestive enzymes and hormones (insulin and glucagon) for blood glucose regulation.

Small Intestine

The small intestine is the primary site for nutrient absorption and digestion.

Esophagus

The esophagus is a muscular tube that transports food from the mouth to the stomach via peristalsis.

Micturition

Micturition is the process of urination, triggered by bladder stretch receptors and controlled by the central nervous system.

Nephron

The nephron is the functional unit of the kidney, responsible for filtering blood and forming urine.

• Juxtaglomerular Apparatus: Regulates blood pressure and filtration rate.

• Loop of Henle: Concentrates urine by reabsorbing water and salts.

• Proximal Convoluted Tubule: Reabsorbs nutrients, ions, and water.

• Peritubular Capillaries: Surround tubules for exchange of substances.

• Collecting Duct: Final site for water reabsorption and urine concentration.

Macula Densa and Granular Cells

Macula densa cells sense sodium concentration in the distal tubule; granular cells secrete renin in response to low blood pressure.

Hormonal Regulation of Renal Function

Key Hormones and Their Effects

Digestive Enzymes and Secretions

Enzymes/Agents and Their Sources

Processes and Comparisons

Sequence of Urine Formation and Elimination

Urine formation begins at the glomerulus and ends with elimination via the urethra.

1. Filtration at glomerulus

2. Reabsorption in proximal tubule

3. Concentration in loop of Henle

4. Secretion in distal tubule

5. Collection in collecting duct

6. Transport through ureter, storage in bladder, elimination via urethra

Heat Stroke vs. Heat Exhaustion

ACE Inhibitors and Blood Pressure

ACE inhibitors lower blood pressure by blocking the conversion of angiotensin I to angiotensin II, reducing vasoconstriction and aldosterone secretion.

• Hormones Involved: Renin, Angiotensin I, Angiotensin II, Aldosterone

• Effects: Decreased blood volume, increased urine output, reduced peripheral resistance

Omega-3 Fatty Acids and HDL

Omega-3 fatty acids and HDL are beneficial for cardiovascular health. Foods rich in omega-3s include fatty fish (salmon, mackerel), flaxseed, and walnuts.

• Benefits: Lower triglycerides, raise HDL, reduce inflammation

Insulin vs. Glucagon

Additional info: Some explanations and table entries were expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.