LECTURE 3

Absorption

The process of taking in nutrients from the GI tract into the bloodstream.

Healthy Diet

A diet that provides the necessary nutrients in optimal proportions for energy, growth, and maintenance of tissues.

Energy Balance

The equilibrium between energy intake and expenditure, crucial for weight maintenance.

Macronutrients

Nutrients required in large amounts for energy and growth, including carbohydrates, proteins, and fats.

Carbohydrates

Molecules like glucose and fructose, which are broken down by amylases for energy.

Proteins

Long chains of amino acids essential for growth and repair, with essential and non-essential types.

Fats

Triglycerides and cholesterol important for energy storage, insulation, and hormone production.

Vitamins and Minerals

Essential micronutrients required in small amounts for various bodily functions.

GI Tract

The gastrointestinal tract, a long tube responsible for digestion, absorption, storage, and waste removal.

Mechanical Digestion

The physical breakdown of food, starting in the mouth with chewing and mixing with saliva.

Growth factors

Essential for repair of mucosa, including ions like sodium chloride, calcium, and phosphates.

Saliva glands

Comprise parotid, submandibular, and sublingual glands, each with specific functions in saliva production.

Saliva composition

Determined by the rate of passage through the glands, affecting its isotonic or hypertonic nature.

Saliva production

Controlled by autonomic system, with parasympathetic stimulation increasing watery saliva and sympathetic control leading to thick, enzyme-rich saliva.

Gastric function

Involves mixing food with acid in the stomach, leading to chyme formation and controlled release into the duodenum.

Nutrient absorption

Occurs mainly in the small intestine, facilitated by structures like villi and microvilli, with various routes like simple diffusion and endocytosis.

Ion absorption

Involves mechanisms like sodium proton exchanger and chloride bicarbonate exchange, crucial for maintaining gut health and function.

Sodium-Potassium Exchange Pump

Responsible for providing the sodium gradient for sodium to enter from the lumen passively.

Glucose Absorption

Involves the sodium-glucose linked transporter 1, allowing two sodium ions to enter for every glucose molecule, setting up a gradient for water absorption.

Oral Rehydration Solution

A solution proposed in the 1960s for dealing with diarrhea cases, based on glucose absorption to facilitate water reabsorption.

Genetic Mutation

Recessive mutation causing a lack of SGLT1 transporter, leading to the inability to transport glucose and galactose, resulting in severe diarrhea and dehydration.

Fat Digestion

Involves the breakdown of fat globules into smaller ones through emulsification by bile salts, allowing lipases to act on them.

Micellar Shell

Fatty acids and monoglycerides lose their micellar shell and pass through the brush border of the duodenum and jejunum by diffusion.

Chylomicron

Structure formed in the lacteals to transport fatty acids and monoglycerides into the lymphatic system and ultimately into the hepatic portal vein.

Water Absorption

Mainly occurs in the small intestine due to the osmotic gradient created by nutrient absorption, with most water being reabsorbed there rather than in the large intestine.

Large Intestine

Functions to store fecal material, absorb sodium and water via the epithelial sodium channel, and is crucial for the synthesis of vitamin K by gut microbes.

Defecation

Involves the movement of feces through the large intestine, aided by mucus, mass movements, and peristalsis, leading to relaxation of the internal anal sphincter and external sphincter for bowel movement.