Digestive system

• The digestive system facilitates food ingestion, breakdown, nutrient absorption, and waste elimination.

Mouth

• The mouth initiates the digestive process through ingestion, mechanical breakdown, propulsion, and digestion.
• It contains saliva to aid in the initial stages of digestion and swallowing.

Esophagus

• This serves as a passageway for food, initiating propulsion via deglutition.

Stomach

• The stomach functions as a temporary storage unit for ingested food, facilitating mechanical and chemical digestion.
• It is capable of liquid absorption.
• It secretes intrinsic factors.
• Protein chemical breakdown takes place here.

Liver

• The liver handles metabolism, storage, and detoxification and produces bile.
• Hepatocytes digest carbs, fats, and protein.

Pancreas

• It provides enzymes necessary for digesting chyme and bicarbonate.
• It breaks down proteins, starch, fat, and nucleic acids.

Gallbladder

• The gallbladder stores bile and absorbs water and ions.

Small Intestine

• The small intestine is the primary site for digestion and absorption, comprising the duodenum, jejunum, and ileum.
• It digests carbs, protein, fat, and nucleic acids

Large Intestine Function

• The large intestine absorbs water and metabolites.
• It functions as a temporary storage and elimination site.

Large Intestine Role in Digestion

• The large intestine is responsible for absorption, digestion via gut bacteria, propulsion, and defecation.

Large Intestine Parts

• The large intestine consists of the cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal.

Innervation of GI Tract

• The enteric nervous system, or "gut brain," manages the GI tract.
• It regulates motility and secretory functions of digestive activity.

Components of GI Tract Innervation

• Reflex arcs respond to internal and external stimuli.
• Parasympathetic inputs enhance digestive activity, while sympathetic inputs inhibit it.

Peristalsis

• Peristalsis involves alternating waves of smooth muscle contraction and relaxation.
• It propels food through the digestive tract.

Segmentation

• Segmentation involves local constrictions of the intestine.
• It mixes food with digestive juices.

Salivary Amylase

• This is is produced by salivary glands.
• It aids in the digestion of carbs in the mouth, breaking down starch through mastication and hydrolysis.

Amylase

• The pancreas secretes amylase.
• It breaks down carbs in the small intestine.

Proteases

• These are secreted by the stomach and pancreas.
• They break down proteins.

Lipases

• Lipases are secreted by chief cells in the stomach.
• They digest lipids in the small intestine, where triglycerides are emulsified to break down large fat globules.

Bile

• The liver produces bile.
• It digests and absorbs fats in the small intestine.

Pepsin

• The stomach produces pepsin.
• It digests protein in the stomach.
• Pepsinogen is activated to pepsin by the acidic environment to prevent the enzyme from digesting itself.

Bicarbonate

• Bicarbonate is produced by the kidneys and RBCs.
• It is used as a buffer system to maintain blood pH.
• It prevents acidosis and maintains metabolic function.

Venous Portion of Splanchnic Circulation

• This is the hepatic portal circulation.

Function of Hepatic Portal Circulation

• It drains nutrient-rich blood from digestive organs.
• Delivers this blood to the liver for processing.

Stomach Structure

• The stomach contains muscular layers for churning and mixing food.
• Rugae allow for expansion.
• Mucosa traps bicarbonate fluid.

Small Intestine Structure

• Circular folds force chyme to spiral through the lumen, slowing movement for increased absorption time.

Villi in Small Intestine

• These create a velvety texture that facilitates nutrient absorption.

Microvilli in Small Intestine

• The brush border completes the digestion of carbs and proteins.

Secretion Made by Stomach Cells

• Hydrochloric acid activates pepsin, denatures proteins, kills bacteria, and secretes intrinsic factors.

Carbs

• Carbs break down into monosaccharides.
• They are absorbed into enterocytes and transported to the liver.

Proteins

• Proteins break down into amino acids.
• Amino acids are absorbed and then transported to the liver.

Lipids

• Lipids break down into monoglycerides and fatty acids.
• These recombine into triglycerides, are packaged into chylomicrons, enter lacteals, and are transported via the lymphatic system.

Fermentation

• It forms short-chain fatty acids that are absorbed and used as fuel.

Vitamin Synthesis

• Vitamin synthesis aids in producing clotting proteins in the liver (vitamins K and B).

Immune System Interaction

• Maintains dynamic equilibrium.

Intrinsic Factor

• Intrinsic factor is needed for the absorption of vitamin B12 in the small intestine.