Physiology and Anatomy 1

• HCL
• Pepsin (Pepsinogen)
• Lipase
• Mucus, HCO_3^- 
• Intrinsic factor

• bacterial effect
• activation of pepsinogen
• denaturation of proteins

• Protein digestion (including collagen, which is only little affected by other preteolytic enzymes)
• denaturation of casein (suckling infants)

• Fat digestion 

• Lubrication
• mechanical protection 
• protection from self digestion 

• Glycoprotein that helps absorption of Vitamin B₁₂

Gastric secretions are triggered by stimuli inside the body --> Hormones, nutrients, sensorimotor ANS loops, and by stimuli from the outside world / brain representations (thoughts of food, conditioned reflexes) 

1. Fundus glands: contain chief cells, parietal cells, ECL cells, mucous neck cells
2. Pyloric glands: secrete mucus and gastrin 

Different cell types make different gastric secretions. These are exocrine glands (salivary etc). Endocrine glands are glands of the endrocrine system that secrete their products,hormones directly into the blood rather than through a duct. 

Just like any other exocrine gland. Secretory cells lining a pipe that opens into stomach. These cells have blood and nerves on one side, and the stomach inside on the other side 

Essentially the same story as peptide neurotransmitters or peptide hormones. 

DNA --> Protein --> pack into vesicles --> exocytosis 

H⁺ / K⁺ exchange pump (ATPase) on the stomach side pumps acid (H⁺) into the stomach. The "left behind" HCO₃^- is transported out into the blood in exchange for Cl^- Ions, which enter the cell and are secreted through Chloride channels into 

the stomach --> HCl in stomach. 

• Endocrine - Gastrin hormone
• Paracrine - Histamine 
• Neural - Acetylcholine 

Acid is rapidly buffered by pancratic secretions to bring stuff (chyme) to a pH of about 7 soon after is leaves the stomach 

Pepsinogen + pepsin: digestion proteins. 

Released into stomach in response to acid, or signals from motor ANS 

Peptide hormone secreted by endocrine cells in stomach, in response to dietary peptides / AAs in stomach lumen. Stimulated acid secretion into stomach 

Helps B_{12 absorption. Vitamin B}12 _{in mouth bound to R-protein --> binding to intrinsic factor.}

_{Lack of intrinsic factor leads to pernicius anemia because of failure of maturation of the red blood cells in the absence of B12 stimulation of the bone marrow.} 

• Digestion of ingested food
• Absorption of digestive producs, electrolytes and water
• Propulsion of chyme and delivery to the larger intestine 

Pancreas releases into small intestine (duodenum) many digestive enzymes, e.g. trypsin (protein), amylase (carbs), lipase (fat) 

Pancrea releases into small intestine (duodendum) an alkaline solution (bicarbonate) which neutralizes acidic stuff coming from the stomach. This pH change (pH > 5) is required for pancreatic enzymes to work. 

Food appears in small intestine: sensed by nerves and endocrine cells in intestine --> motor ANS signals (Ach) and hormones (CCK, gastrin) are released and act on pancreas. 

Pancreas secretes digestive enzymes and bicarbonate is released from pancreas into small intestine. 

• Food appears in the small intestine and is sensed by the endocrine cells in the intestine
• Hormones (CCK, secretin) are released and act on liver
• The liver releases bile into the small intestine
• Bile emulsifies fat
• Bile also contains liver waste (billirubin, cholesterol) that gets excreted

• They are small stones mostly made of cholesterol
• They form in the gallbladder when too much water is absorbed from bile 

• Liver and pancreas are not the only sources of secretion in intestine
• Different cell types in intestine wall release further things that re important for safe and efficient digestion: mucus, H₂O, Antimicrobials 

Macro- and micro-scopic anatimical folds in anatomical folds on intestine surface massively increase surface area = helps absorption 

Na / K ATPase pumps Na⁺ into blood side --> low intracellular [Na+]

Diffusion force sucks Na⁺ from intestine side via channels and transporters 

Water just follows ions by osmosis 

Different "carb-breakdown" enzymes sit on gut side membranes of intestinal lining cells. They break down compley carbs into smaller sugars: glucose, fructose, galactose.

The latter are then transported into lining cells, and from there into blood. 

Simple sugars are moved from gut into blood by secondary active transporter (Na⁺-sugar cotransporter proteins, eg SGLT) and/ or by facilitated diffusion (sugar ferry proteins)

Proteins are progressibely broken down to amino-acids by enzymes in stomach, pancreas and small intestine cells 

Same concepts as sugars absorption: secondary active transporters (Na⁺-powered) & passive transporters 

Emulsified by liver bile acids: hydrolyzed by pancreatic lipases into monoglycerides and free fatty acids --> these diffuse into cells 

Absorption: Monoglycerides and free fatty acids--> made into chylomicrons (lipid-protein blobs) in intestinal lining cells --> endocytosed into lymphatic systems 

Gi hormones inform the body about the arrival of nutrients. The composition of the GI peptide cocktail released refelcts the amount and composition of the meal. GI hormone functions extend well beyond the control of GI functions (secretion and motor functions), they control appetite for example. 

Stimulated by binding of food components to extracellular receptors (receptors on gut side) or by other hormones and neurotransmitters (receptors of blood side) 

Parasympathetic motor ANS: increases GI motility and secretions