Human Biology: Small Intestine Functions

Digestion Process

• Small Intestine: Absorbs most of the water before food moves to the colon. Minute fat globules enter the lacteals.
• Colon: Absorbs water and mineral salts from undigested food. Ferment vitamins with colonic bacteria (e.g., vitamins B and K).

Adaptations of the Small Intestine for Absorption

• Villi: Finger-like projections that increase the surface area for faster absorption of digested food.
• Blood Capillaries: Allow blood to quickly transport absorbed glucose and amino acids, maintaining a diffusion gradient.
• Lacteals: Allow rapid transport of absorbed fats, maintaining a steep diffusion gradient.
• Epithelium (Wall): One-cell thick, providing a short diffusion distance for absorbed food.
• Microvilli: Increase surface area for absorption.
• Mitochondria: Provide energy for active transport of nutrients into the villi.

Assimilation

• Glucose: Assimilated and broken down during cellular respiration to release energy for cell functions. Excess glucose is stored as glycogen.
• Protein: Amino acids are used to build new cytoplasm for growth and repair of cells, form enzymes and hormones. Excess amino acids are deaminated in the liver.
• Fats: Absorbed into lymphatic capillaries, which discharge fat into the bloodstream.
  • Fats are used to build protoplasm if glucose is abundant.
  • Fats are used to provide energy if glucose is scarce.
  • Excess fats are stored in adipose tissue.

Egestion

• Rectum: Temporarily stores faeces.
• Anus: Ejects faeces when the rectum contracts.

Role of Other Organs in Digestion

• Pancreas: Produces pancreatic juice containing enzymes (amylase, protease, lipase) that are secreted by the pancreatic duct into the small intestine.
• Bile Duct: Secretes bile into the small intestine.
  • Bile salts emulsify fats by breaking them into smaller droplets, increasing the surface area for lipase activity.
• Liver:
  • Hepatic Portal Vein: Transports blood rich in amino acids and glucose from the small intestine to the liver.
  • Hepatic Vein: Distributes remaining amino acids and glucose to body parts.
  • Hepatic Artery: Transports blood rich in oxygen to the liver.
  • Production of Bile: Helps digest fats.
  • Deamination of Amino Acids: Removes amino groups from amino acids and converts them to urea.
  • Detoxification: Removes harmful substances like alcohol and benzoic acid.
  • Glucose Regulation: Regulates blood glucose concentration.

Effects of Alcohol Consumption on the Brain

• Temporary Effects:
  • Increased reaction time.
  • Reduced self-control leading to risky behavior like drunk driving.
  • Blurred vision, poor judgment, and poor coordination.
• Long-Term Effects:
  • Increased risk of gastric ulcers.
  • "Wet Brain" (dementia).
  • Shrinkage of brain volume.
  • Fetal brain development problems during pregnancy.
  • Liver cirrhosis (liver cells destroyed and replaced with fibrous tissue) leading to liver failure.
• Societal Implications:
  • Neglect of work and family.
  • Violent behavior.
  • Increased criminal activity.

Starch Test, Benedict’s Test, Biuret Test, Fats test

• Starch Test: Turns from orange to blue-black if starch is present. Remains orange if absent.
• Benedict’s Test: Turns from blue to red if reducing sugars are present. Remains blue if absent.
• Biuret Test: Turns from blue to violet if protein is present. Remains blue if absent.
• Fats Test: Forms a milky solution if lipid is present.

Homeostasis & Hormones

• Definition: Maintaining a constant internal environment.
• Negative Feedback Process: A mechanism to regulate internal conditions by reversing any changes made to maintain a stable state.

Blood Glucose Regulation

• Increase in Blood Glucose: Beta cells in the islets of Langerhans secrete insulin. Insulin increases cell permeability to glucose, stimulating glucose uptake and cell respiration. Excess glucose is converted to glycogen. Blood glucose concentration returns to normal.
• Decrease in Blood Glucose: Alpha cells in the islets of Langerhans secrete glucagon. Glucagon stimulates the conversion of glycogen to glucose. Blood glucose concentration returns to normal.

Water Potential Regulation

• Increase in Water Potential: Osmoreceptors in the hypothalamus detect the change. The hypothalamus signals the pituitary gland to decrease ADH production. Decreased ADH lowers the permeability of the collecting duct to water, decreasing water absorption. Blood potential returns to normal.
• Decrease in Water Potential: Osmoreceptors in the hypothalamus detect the change. The hypothalamus signals the pituitary gland to increase ADH production. Increased ADH increases the permeability of the collecting duct to water, increasing water absorption. Blood potential returns to normal.

Skin Temperature Regulation

• Increase in Skin Temperature: Thermoreceptors in the skin detect the change. Arterioles dilate, increasing blood flow to the skin for heat loss. Sweat glands increase sweat production for evaporative cooling. Skin temperature returns to normal.
• Decrease in Skin Temperature: Hair erector muscles contract, causing hair to stand on end to trap heat.

Diabetes

• Definition: A condition where blood glucose concentration cannot be regulated.

Diabetes

• Blood glucose concentration exceeding the kidneys’ reabsorption capacity results in glucose being excreted in urine.
• Type 1 diabetes is inherited and characterized by the inability of the Islets of Langerhans to produce or secrete sufficient insulin.
  • Management involves regular blood glucose and urine testing, careful diet, and regular insulin injections.
• Type 2 diabetes risk factors include:
  • Obesity: Liver and muscle cells exhibit insulin resistance.
  • Age: Liver and muscle cells exhibit insulin resistance.
  • Family history: Inherited risk.
  • Blood lipid levels: High LDL and low HDL cholesterol levels.
  • Sedentary lifestyle: Physical activity controls weight, utilizes excess glucose, and maintains insulin sensitivity in liver and muscle cells.

Excretion

• Excretion is the removal of metabolic waste, toxic substances, and substances in excess of the body’s needs.
• Excretion is essential because metabolic activities produce harmful or toxic substances that are not required by the body.
• Metabolic waste/excretory products must be removed from the body.

Osmoregulation

• Osmoregulation maintains a constant water potential by controlling the water potential and solute concentration in the blood involving the kidneys and skin.
• Excess amino acids are deaminated to urea in the liver.
• Ultrafiltration: High blood pressure in the afferent arteriole, larger than the efferent arteriole, forces small, soluble substances like water, urea, and amino acids into Bowman’s capsule to form glomerular filtrate.
• Proximal convoluted tubule: Amino acids and glucose are selectively reabsorbed through diffusion and active transport from the glomerular filtrate.
• Distal convoluted tubule and loop of Henle: Water and mineral salts are reabsorbed.
• Collecting duct: Water is reabsorbed from the urine.
• Formed urine is removed via the urethra.

Eye

• Sclera: Tough, white outer covering of the eyeball, continuous with the cornea. Protects the eye from mechanical damage.
• Conjunctiva: Thin transparent membrane covering the sclera in front. Mucous membrane secreting mucus, keeping the front of the eyeball moist.
• Eyelashes: Shield the eye from dust particles.
• Eyelid: Protects the cornea from mechanical damage. Squinting helps prevent excessive light entry.
• Tear gland: Secretes tears for various functions:
  • Washing away dust particles.
  • Keeping the cornea moist for dissolved oxygen diffusion.
  • Lubricating the conjunctiva, reducing friction during eyelid movement.
• Iris: Controls pupil size, regulating light entering the eye.
• Pupil: Hole in the center of the iris allowing light entry.
• Ciliary body: Contains ciliary muscles, regulating lens curvature/thickness.
• Suspensory ligament: Connective tissue attaching the lens edge to the ciliary body.
• Aqueous humor/chamber: Maintains eyeball firmness and refracts light into the pupil.
• Vitreous humor: Transparent, jelly-like substance behind the lens. Maintains eyeball firmness and refracts light onto the retina.
• Cornea: Dome-shaped layer continuous with the sclera. Refracts light rays into the eye, causing the greatest refraction.
• Lens: Elastic, changes shape/thickness for focusing light onto the retina.
• Choroid: Middle layer of the eyeball. Contains blood vessels transporting oxygen and nutrients to the eyeball, and removing metabolic waste products. Pigmented black to prevent light reflection within the eye.
• Retina: Innermost layer of the eyeball. Light-sensitive layer forming images, containing photoreceptors producing nerve impulses when stimulated and connected to the optic nerve. Nerve impulses are transmitted from the optic nerve to the brain.
• Fovea: Small yellow depression in the retina. Where images are typically focused. Contains the highest density of cones but no rods, enabling detailed color vision in bright light.
• Blind spot: Region where the optic nerve leaves the eye. Contains no rods or cones, not sensitive to light. Cannot see objects whose image falls on the blind spot.
• Optic nerve: Transmits nerve impulses from photoreceptors to the brain when stimulated.

Forming an image on the retina

• The cornea and aqueous humor refract light rays onto the lens.
• The lens further refracts and converges the light rays on the retina.
• The image on the retina stimulates the photoreceptors.
• The image formed is upside down, laterally inverted, and smaller.
• Nerve impulses are produced by the photoreceptors and transmitted via the optic nerve to the brain.
• The brain interprets these nerve impulses, allowing us to see the object upright, front to back, and in the correct size.

Accommodation/Focusing

• Adjustment of the lens to form clear images of objects at different distances on the retina.
• Far object:
  • Ciliary muscles relax, pulling on the suspensory ligament.
  • Suspensory ligament becomes taut, pulling on the lens edge.
  • Lens becomes thinner and less convex.
  • Refracts light onto the retina to produce a focused image of the far object.
• Near object:
  • Ciliary muscles contract, relaxing their pull on the suspensory ligaments.
  • Suspensory ligament slackens and becomes less taut, relaxing their pull on the lens edge.
  • Lens becomes thicker and more convex.
  • Refracts light onto the retina to produce a focused image of the near object.

Pupil Reflex: Bright light

• Circular muscles of the iris contract.
• Radial muscles of the iris relax.
• Pupil constricts to reduce light entering the eye, producing a focused image.

Pupil Reflex: Dim light

• Radial muscles of the iris contract.
• Circular muscles of the iris relax.
• Pupil dilates to allow more light into the eye, producing a focused image.

Advantages of pupil reflex

• Protective reflex.
• Regulates light entering the eye, preventing damage to photoreceptors and ensuring optimal image formation.

This quiz delves into the critical roles of villi and microvilli in human digestion within the small intestine. Test your knowledge on nutrient absorption, diffusion gradients, and the functions of blood capillaries and lacteals. Understand how these structures contribute to effective nutrient uptake.