Digestive system and the liver

Give me an overview of digestion?

Oral cavity has salivary glands(pH neutral): Digestion starts with chewing and salivary amylase helps break down the carbohydrates. Lipase(a little) start to break down the fat. Mucus helps make food easier to swallow.

Esophagus: This is a tube that carries the food into the stomach through peristalsis.

Stomach peristaltic contraction motility(acidic pH 1.5-2): (Fundus→Body→Antrum)Stores the food and also starts to break down the food (Pepsinogen and lipase from chief cells helps digest proteins and HCl from parietal cells helps kill bacteria). The stomach then mixes up the food food to make it into a paste called chyme. We also have mucous and bicarbonate from mucous cells. And gastrin from gastrin cells and histamine. Digest proteins and fats minimally. ABSORBS acohol and asprin…

Pylorus: Is the bottom part of the stomach that helps empty the food into the SI.

SI(neutral pH) mixes by segmental contraction: (Duodenum→ jejunum→ ilium) Nutrient absorption happens. Duodenum recieves the bile from the liver and enzymes from pancreas. Jejunum is the major nutrient site. And ilium is what absorbs the rest of the nutrients. Digests polypeptides, carbs, fats, nucleic acids. Sooo SI digests everythign except proteins.

LI(segmental motility): Absorbs water and electrolytes and forms and stores feces. Digests nothinggg. secretes mucous through goblet cells. Absorbs ions, mineral, water, vitamins, organic molecules,

Rectum: Is where you store feces

Anus with external anal sphincter: controls release of feces.

Our accessory organs:

-Liver: Makes bile to break down the fats

-Pancreas: Make enzymes and bicarbonate to help reduce stomach acidity

-Gallbladder stores the bile

What is the Mucosa?

The mucosa is the lining of the GI tract that comes into direct contact with the chyme. It is created by mucosal epithelium and lamina propria(AKA connective tissue) and musculoris mucosae.

What modifications in the digestive system help with surface area?

Rugae(in the stomach) it helps flatten out the folds while it expands and plicae in the SI that slows down the food for max absorbtion of nutrients. We also have vili and crypts and Submucosal Glands in the intestines and in the stomach we have gastric glands .

What are PEYER’S PATCHES & GALT?

Peyer’s patches and galt are immune structures in the ileum which are clusters that detect bacteria or viruses so they are very important in gut immunity.

What is the SUBMUCOSA?

The submucosa is a thick layer of connective tissue under the mucosa. It supports the mucosa and it houses blood vessels and lymphatic vessels. It also the submucosal plexis of the enteric nervous system. It controls secretion and local blood flow and mucosal movement.

What is Muscularis externa?

It is 2 layers smooth muscles that are responsible for gut movement. This contains the Myenteric plexis this is also of the enteric nervous system. it helps with muscle contrations for movement.

What is the Serosa?

It is the outermost layer of the GI tract it is a continuation of the peritoneal cavity. It ends up forming sheets of mesentery which helps intestines not get tangled.

What are the 4 basic processes of digestion?

Digestion, Secretion, Absorption, and Motility

What are the challenges that the digestive system could face?

-Avoiding Autodigestion

-Mass balance

- Fluid loss through diarrhea or vomiting

-Defense against pathogens

Secretion in the digestive system?

Digestive enzymes get secreted in the mouth, stomach, and intestines. Mucus is secreted by mucous cells in the stomach, serous cells in the salivary glands, and goblet cells secrete mucous into the intestines.

Motility in the digestive system?

Tonic contractions for minutes to hours they are important because they keep the bolus from moving backwards. Tonic contractions occur in smooth muscle sphincters and the anterior part of the stomach.

Phasic contractions that last only a few seconds. They occur in the posterior region of the stomach and also in the SI. Slow wave potentials cause the phasic contractions Special cells called Interstitial Cells of Cajal start the waves. They do peristalsis(contraction responsible for forward movement of the bolus) and segmental contractions(contraction responsible for mixing).

Enteric Nervous System(ENS)

The ENS also known as the little brain of the gut.

• Has intrinsic neurons, they handle local reflexes like secretion or motility.

• extrinsic neurons that are autonomic and bring signals from the CNS to the digestive system they activate or inhibit digestion.

• Neurotransmitters and neuromodulators.

• Glial Support Cells protect ens neurons

• Diffusion barrier protects ENS neurons, like brain's blood-brain barrier.

What are integration centers?

Integration centers are basically like structures that help decide what the GI tract should do. The ENS has 2 types of reflexes. The short reflex is integrated into the ENS because it is triggered by the local stimuli and the long reflex is integrated into the CNS.

What are the 4 digestive hormones?

GI PEPTIDES: HORMONES OR PARACRINE SIGNALS

GASTRIN FAMILY: GASTRIN(in stomach stimulates acid production) AND CHOLECYSTOKININ (CCK stimulates contraction and secretion of enzymes but inhibits gastric emptying and acid secretion)

SECRETIN FAMILY: SECRETIN(promotes acid Hco3-, VASOACTIVE INTESTINAL PEPTIDE (VIP),

GLUCOSE-DEPENDENT INSULINOTROPIC PEPTIDE (GIP), AND GLUCAGON-LIKE PEPTIDE-1 (GLP-1)

MOTILIN

Mastication

chewing

Deglutation

Swallowing

What happens during the deglutation reflex?

1. During the deglutition reflex the tongue pushed the bolus against the soft palate and the back of the mouth in order to trigger the swalloing reflex.

2. As the bolus is pushed at the back of the mouth, the breathing is inhibited because the epiglottus folds down to make sure that the bolus does not get into the airway. The upper esophogeal muscle relaxes.

3. The food moves down the esophagus by peristaltic waves and gravity.

The stomach has 3 functions, what are they?

Storage, digestion( breakdown of lipids and proteins by gastrin and lipase), DEFENSE AGAINST SWALLOWED PATHOGENS, DIGESTIVE ACTIVITY IN THE STOMACH BEGINS WITH THE LONG VAGAL REFLEX (preparing the stomach by stimulating secretions and motility even before food arrives)OF THE CEPHALIC PHASE(sight, smell, taste, or thought of food)

What are the GASTRIC SECRETIONS?

• PEPSINOGEN FROM CHIEF CELLS

• MUCUS AND BICARBONATE FROM MUCOUS CELLS

• SOMATOSTATIN FROM D CELLS

• HISTAMINE FROM ECL CELLS

• GASTRIN FROM G CELLS

• HCL FROM PARIETAL CELLS

Oxyntic Gland does what?

1. Oxyntic glands

•• Oxyntic/parietal cells: acid secretions

•• Peptic/chief cells need to be activated by pepsin: pepsinogen

Mucous neck cells

Pyloric Gland does what?

Have G(secrete gastrin which stimulates gastric acid) and D cells(secrete somatostatin that inhibit gastric acid secretion)

CEPHALIC AND
GASTRIC PHASE
REFLEXES

I see food and the medulla oblangata gets activated and it sends a signal to the preganglionic presympathetic neuron LONG REFLEX into the enteric system SHORT REFLEXES from now, postganglionic presympathetic neuron and intrinsic enteric neurons catch the signal and send it to the target cell which results in secretion and motility.

However, short reflexes can also be initiated by distension or peptides and amino acids.

Cephalic phase

Food or cephalic reflexes (sight, smell, thought of food) trigger the stomach to start secreting:

• Gastrin

• Histamine

• Hydrochloric acid (HCl)

What does Gastrin do?

Gastrin helps the stomach make acid.

It does this in two ways:

• Directly, by telling parietal cells to make acid.

• Indirectly, by causing the release of histamine, which also increases acid.

The acid then causes the stomach to release pepsinogen, which helps digest proteins.

When there’s too much acid (H⁺), the stomach releases somatostatin, a signal that slows down the release of both acid and pepsin.

What happens in the intestinal phase of digestion?

• The SI is where most of the digestion happens. Carbs and proteins are absorbed as monosaccharides and small peptides. And the lipid digestion depends on the bile salts lipases get absorbed by lacteal ducts. Nucleain acids are digested into monosaccharides and nitrogenous bases.

• The Pancreas has 2 jobs:

  Endocrine: secrete insulin and glucagon

  Exocrine: secrete bicarbonate and digestive enzymes into SI. Also the digestive enzymes are released by the pancreas in their inactive form zymogens and get activated once in the SI.

• The liver makes bile using speacial cells called hepatocytes to digest fat. The bile is made up of bile salts, bile pigments, and cholesterol! The bicarbonate from the pancreas’ exocrine function helps neutralize the bile. The gallbladder stores the bile and concentrates it until needed by the body. The bile moves through the hepatic duct from the liver and into the SI by common bile duct.

• Goblet cells make mucus in the Large intestine to help things run smoothly and the gut also makes isotonic nacl fluid to make things mix better.

How does the isotonic Nacl secretion take place?

1. Na+ cl+ K+enter the Intestinal cell by a cotransporter

2. Cl- gets into the lumen by CFTR

3. Na+ is reabsorbed into the interstial fluid!

4. Cl- in the lumen attracts Na+ through paracellular pathway and the water follows.

True or False? Trypsinigen is activated to trypsin using brush broader enteropeptidase

True

How does bicarbonate get secreted from the pancreas?

1. Cells that make

   bicarbonate have

   a lot of carbonic

   anhydrase (CA)

2. Chloride enters cells

   by indirect active

   transport and leaves

   the apical side

   through a CFTR

   channel into the lumen of the pancrease or intestine. Cl- then

   reenters the cell in

   exchange for HCO3-.

3. Leaky junctions allow

   paracellular

   movement of ions

   and water. Negative

   ions in the lumen

   attract Na- by the

   paracellular pathway.

   Water follows.

Liver

the liver is an organ right below the diaphragm towards the right side of the body. Fun fact: Liver is one of the largest organ in the adult body, weighing 3.3 lb! Its right lobe is bigger than its left lobe. It gets 75-85% of its blood from the portal vein. The liver gets nutrients and metabolite rich blood and excretes some of this in the bile and stores and metabolizes some of it. Somethings are waste that need to be excreted by the kidneys by the others are useful nutrients like glucose.

Common hepatic duct

Is something that takes the bile made in the liver to the gallblader for storage.

Common bile duct

The common bile duct takes the bile from the gallbladder into the small intestine.

Hepatic artery

brings the oxygenated blood to the liver. This blood contains metabolites

Hepatic Portal Vein

The hepatic portal vein takes away the blood from the liver. The blood in it is very nutrient rich and also have hemoglobin in it.

Sphincter of oddi

Controls release of bile into the SI duodenum from the pancreas

Antechamber of the heart

The antechamber of the heart collects all the blood from the portal vein from the liver.

Hepatocytes

Hepatocytes are speacialized liver cells that 70% face the sisunoids (in which the blood flows)which helps blood exchange betweeen the cells be better.

Liver

• METABOLIC

• STORAGE

• EXCRETORY

- SECRETORY

• PROTECTIVE

• CIRCULATORY

• COAGULATION

MESS PCC

Metabolism fuctions

CARBOHYDRATE METABOLISM

-GLUCONEOGENESIS

- GLYCOGENOLYSIS AND GLYCOGENESIS

• SYNTHESIS OF FATTY ACIDS, LIPOPROTEINS, CHOLESTEROL

• KETOGENESIS (BREAKDOWN OF FATTY ACIDS TO KEYTONES)

• PROTEIN METABOLISM

• SYNTHESIS OF PLASMA PROTEINS (ALBUMIN, GLOBULIN, FIBRINOGEN)

• UREA SYNTHESIS (AMMONIA TO UREA)

• HORMONE METABOLISM

• RED BLOOD CELL PRODUCTION (IN FETAL LIVERS DURING THE FIRST

TRIMESTER OF PREGNANCY)

STORAGE FUNCTIONS

GLYCOGEN

•• VITAMINS

-A, D, E, K (LIPID SOLUBLE)

-B12 (WATER SOLUBLE)

•• IRON

•• COPPER

EXCRETORY/SECRETORY FUNCTIONS

BILE

• WATER

• CHOLESTEROL

• BILE PIGMENTS (BILIRUBIN AND BILIVERDIN)

• ANIONS OF THE BILE ACIDS

• PHOSPHOLIPIDS (MAINLY LECITHIN)

• BICARBONATE AND OTHER IONS

• INSULIN-LIKE GROWTH FACTOR 1 (IGF-1)

• MOST BLOOD PROTEINS

• CHOLESTEROL, FATTY ACIDS

PROTECTIVE FUNCTION of liver

The liver protects by purifying, transforming, and clearing endogenous/exogenous chemicals. Kupffer cells are special immune cells in the liver that are macrophages that destroy the bacteria and foreign material from the portal blood.

COAGULATION function of the liver

The liver helps in coagulatin by making speacial clotting proteins:

• Fibrinogen I(helps make a clot mesh)

• Prothrombin II(Turns into thrombin which starts clotting)

• Other clotting factors: V, VII, IX, X, XI – all help the clotting process work right

• Proteins S and C make sure cotting doesn’t go too far

• Antithrombin also slows down the cotting so that the clots don’t become too big

What are Liver enzymes and how do they tell us about the liver function?

Liver enzymes from damaged liver cells(Hepatocytes) show up when the liver is dying TRANSAMINASES enzymes,

AST (also called SGOT)

ALT (also called SGPT)

High levels of AST/SGOT or ALT/SGPT means the liver is damaged.

CHOLESTATIC ENZYMES (FROM INJURED bile duct)

• High levels of (ALP) or (GGT) tell us thta the bile duct is damaged.

Enterocytes

Enterocytes transports ions and nutrients. Capillaries transport absorbed nutrients.Goblet cells secrete mucus. Lacteals transport fats to the lymph.

What do stem cells do

Stem cells divide to replace damaged cells.

What do the crypt do?

Crypt cells secrete ions and water.

What do the endocrine cells do?

Endocrine cells secrete hormones.

CCK

CCK is in the pancreas. Inhibits acid secrection in stomach.

Muscularis mucosae

2 Layer of smooth muscle do motility

Chyme path into the SI

Food goes into stomach acid gets secreted there is gastric motility and make chyme. Chyme enters the SI. When food enters the SI, there are 3 ways the body can react.

1. Enzyme + Bicarbonate Secretion helps digest food and neutralize stomach acid.

2. Slows Down the gastric digestion (feedback):Chyme tells the stomach to chill — slow acid, enzyme release, and movement. It also prevents overload in the small intestine

3. Starts Insulin Release (feedforward):

   Carbs trigger hormones GIP and GLP-1 and tell pancreas to release insulin early (before sugar hits the blood).

Digestion and absorption of fats

Bile salts surround the lipid droplet. The hydrophobic side touches the lipids and the polar side associates with water it becomes emulsions. The pancreatic lipase and colipase breaks down the fats into monoglycerides and fatty acids stored in micelles. Monoglycerides and fatty acids move out the micelles and enter the cell by diffusion. The cholesterol is transported in the cells. The absorbed fats combine with cholestrol and proteins in the intestinal cells to make chylomicrons. Chylomicrons are then removed from the lymphatic system.

Digestion and Absorption of carbohydrates.

Carbs get broken down into monosaccharides the carbs then get absorbed into the small intestine. Proteins break down to amino acids and enzymes for protein digestion.

Free Amino Acid Absorption

Amino acids need help getting into the intestine so they need to use carrier systems like different carriers for Neutral AA, Basic AA, Acidic AA, Imino AA and some need energy since it moves against the gradient. Sodium helps move in with the AA and they both ride in with a carrier protein.

Peptide absorption

The peptide is the form that protein is absorbed in the most. This is faster than the free AA absorption. Active transport needs energy. Metabolized into a free AA in enterocyte only free AA is absorbed by the blood.

Ion and water absorption

Paracellular pathway or trancellular pathway by vit d3. Na+ enters cells by many pathways. The Na+K+ATPase pumps Na+ into the ECF.

Large intestine in inestinal phase

LI concentrates waste. Motility in LI and mass movemement moves bolus forward to trigger defecation reflex. Digestion and absorption of LI. Can cause flatus. Diarreha causes dehydration.

What are the immune functions?

M cells: Check what is in the gut and sample the contents

Immune cells respond by releasing cytokines which call more immune cells for help and start inflammation and increase chloride water and mucus to flush out any threats vomiting helps protective reflex. Also peryer’s patch is for immune system in the mucosal immune system.