Functioning Systems: Food Assimilation

Functioning Systems

• The presentation is on Functioning Systems, specifically Food Assimilation, by Prof. Dr. Eman Salah Abdel-Rehim.
• The presentation covers the digestive system, digestion, types of digestion (mechanical and chemical), expressions related to mechanical digestion, the process of chemical digestion, absorption, metabolism, and the urinary system.

Learning Objectives (Food Assimilation)

• Students will understand the general function of the Digestive System.
• Students will know about Mechanical and Chemical Digestion.
• Students will understand the simplest forms of nutrients and their absorption.
• Students will learn simple outlines about Metabolism.

Functions of Digestive System

• The digestive system breaks down food into smaller molecules.
• The absorbed molecules are transported throughout the body.
• Wastes are eliminated from the body.

How the Body Gets Energy from Food

• Digestion is the process where the body breaks down food into small nutrient molecules.
• It begins in the digestive system, starting in the mouth.

Types of Digestion

• Mechanical Digestion: Physically breaking down food.
  • Begins when taking the first bite of food.
  • Cutting by teeth is the first stage.
• Chemical Digestion: The body breaks foods into smaller chemical building blocks, using chemicals.
  • Begins in the mouth.

Mechanical Digestion Expressions

• Mastication: Chewing and enzymatic breakdown by saliva.
• Deglutition: Swallowing, voluntary in the mouth, and involuntary in the esophagus.
• Churning: In the stomach, forming chyme.
• Peristalsis: Contraction of circular muscle.
• Segmentation: Contraction of longitudinal muscle (backward and forward movement) to the colon.

Chemical Digestion Digestive Juices

• Saliva: From parotid, sublingual, and submandibular glands.
• Gastric Juice: Chief cells make pepsinogen, and parietal cells make HCl.
• Pancreatic Juice: Exocrine cells of the pancreas.
• Bile: Produced by the liver, stored in the gall bladder, and secreted into the small intestine aiding lipid digestion.
• Intestinal Juice: Secreted by the mucosa of the small and large intestine.

Chemical Digestion (Enzymes)

• Mouth: Carbohydrates—salivary amylase
• Stomach: Proteins—pepsin
• Small Intestine: Lipids
• Trypsin, chymotrypsin, amylase and lipase (from pancreas)
• Maltase, sucrase, lactase and peptidases (from intestinal villi)

Absorption

• After digestion, the simplest forms of food (glucose, amino acids, fatty acids) are absorbed.
• Absorption occurs through the intestinal mucosa into the blood.
  • Amino acids and glucose are transported through secondary active transport.
  • Fatty acids go into lymph via simple diffusion.

Metabolism

• Catabolism:
  • Hydrolysis—breaks down polymers into monomers
  • Cellular respiration—oxidation of monomers to yield energy
• Anabolism:
  • Cell maintenance and repair
  • Growth
  • Formation of secretions
  • Nutrient reserves

Metabolism Processes

• Glucose
  • Catabolism: glycolysis, Krebs' cycle, electron transport chain.
  • Anabolism: glycogenesis, gluconeogenesis.
• Fatty Acids
  • Catabolism: Beta-oxidation, Krebs' cycle, and electron transport chain.
  • Anabolism: lipogenesis
• Amino Acids
  • Catabolism: deamination, Krebs' cycle and electron transport chain.
  • Anabolism: synthesis of nonessential amino acids.

Urinary System

• The presentation also introduces the urinary system.
• Learning objectives for the Urinary System include: functions of the urinary system, anatomy of the urinary system, nephron structure, urine formation (filtration, reabsorption, secretion), urine composition.
• Factors affecting kidney function are also discussed.
• Renal dialysis and transplantation as treatments for kidney diseases, as well as the date of the first human transplantation are mentioned.

Functions of the Urinary System

• Regulate blood composition and volume to maintain homeostasis.
• Disposing of metabolic wastes (urea, creatinine, ammonium, uric acid).
• Maintaining water-salt and electrolyte balance (sodium, potassium, bicarbonate).
• Maintaining acid-base balance (blood pH ≈ 7.4).

Urinary System Structure & Anatomy

• Kidneys
• Ureters
• Bladder
• Urethra

Kidney Anatomy

• Protected by fibrous tissue, fat, muscle, and ribs.
• Consists of renal cortex, medulla, and pelvis (including minor and major calyxes)

Nephron

• The structural and functional unit of the kidney.
• Composed of glomerular capsule, capillary network (glomerulus), renal tubules (proximal convoluted tubule, loop of Henle, distal convoluted tubule)

Steps in Urine Formation

• Filtration: removes water and small molecules from blood, in the renal capsule.
• Reabsorption: water and essential molecules are returned to the blood from the renal tubules.
• Secretion: wastes and excess salts are added from body fluids into the tubule fluid (urine) in the renal tubules.

Glomerular Filtration Rate (GFR)

• Amount of filtrate produced per minute by the kidneys.
• About 20% of total blood plasma—enters the kidneys every minute (approx 1000-1200ml/min).
• 625 ml plasma only pass as filtrate.
• Approximately 125-130ml of this filtrate passes through the renal tubules.

Glomerular Filtration Rate Formula:

• Calculation for GFR in liters per day.
• Kidneys can filter about 150-200 liters of plasma per day.

Forces Affecting Filtration

• Glomerular capillary hydrostatic pressure (GHP): +55 mmHg
• Blood osmotic (colloidal) pressure (BOP): -30 mmHg
• Capsular hydrostatic pressure(CHP): -15 mmHg
• Net filtration pressure: ≈+10mmHg

Reabsorption

• Reabsorption of water, nutrients, and electrolytes via different transport mechanisms through the renal tubules, primarily in the PCT, Loop of Henle , and DCT.

PCT Reabsorption — "Obligatory Reabsorption"

• Glucose and amino acids are pumped out of the tubules and also reabsorbed into the blood.
• The transporters are limited and can become saturated if glucose concentrations rise above 180 mg/dl. (Glucosuria)

PCT Reabsorption

• 70% of sodium and water are reabsorbed.
• Chloride follows sodium by simple diffusion.
• Positively charged ions draw chloride out of the filtrate.
• Some compounds present in high concentration in the filtrate go into the blood by diffusion.

Loop of Henle — Reabsorption

• Descending loop: permeable to water, water moves out of the tubule due to the osmotic gradient.
• Ascending loop: thick epithelium, impermeable to water, pumps out sodium.

So, why is the Loop of Henle useful?

• The longer the loop, the deeper it travels into the hyperosmotic medulla. This allows for more reabsorption and concentrated tubular fluid.

DCT and CT - Reabsorption “Facultative-Reabsorption"

• Reabsorption depends on the body's needs.
• DCT and CT walls have tight junctions, impermeable to water.
• Cells have ADH (antidiuretic hormone) and Aldosterone receptors that modify water/ion permeability according to needs

Regulation of ADH Secretion

• ADH increases water retention reducing urine volume and prevents dehydration.
• Affected by decreased blood volume and blood pressure by Baroreceptors and increased salt concentration by Osmoreceptors.

DCT and CT Reabsorption (Urine Concentration)

• Late distal tubule is impermeable to water, with low ADH.
• When ADH is released from the posterior pituitary, aquaporin channels open. More water is thus absorbed.

Secretion and Excretion

• Secretion: Selective transport of molecules from blood in peritubular capillaries into filtered fluid in the tubular lumen.
• Waste products like urea, excess metabolites, K+, H+, and Ca++
• Excretion: The body removes urine (molecules dumped outside the tubules).

Urine Formation Summary

• Key stages and direction of urine formation, as well as proportion of amount in different stages.

Urine Composition

• 95-96% water
• Urea, uric acid, amino acids, electrolytes

Daily Urine Production

• Average urine production (600ml-2500ml/day)

Factors Affecting Kidney Function

• ADH: prevents excess water loss.
• Alcohol: inhibits ADH secretion, more urine volume, and diluted.
• Aldosterone: prevents sodium and water loss.
• Caffeine: increases the rate of salt and water loss.
• Increased blood pressure: increases the rate of water loss.

Kidney Diseases

• Affect structure and function through stages, which can lead to failure.
• Kidney failure is fatal, but it can be treated by dialysis or transplantation.
• Kidney is the first successfully transplanted organ in humans (1954).

Hemodialysis

• A treatment for people with kidney failure.
• The kidneys filter the blood, removing wastes and toxins.
• Dialysis works by using a dialyzer with a thin membrane to separate the patient's blood from a dialysis solution.
• Waste products move from the blood into the dialysis solution by diffusion due to the concentration gradient.
• Essential minerals and amino acids move from the dialysis solution into the blood.