Digestion and Absorption Flashcards
Protein digestion begins in the ____ with ________
Stomach, pepsinogen/pepsin
What is the role of hydrochloric acid (HCl) in the stomach?
-Activates pepsinogen into pepsin (to digest proteins)
-Lowers pH, which helps to initially denature proteins
-Kills pathogenic bacteria and fungi in ingested foods
Gastrin
Secreted into the bloodstream, causes stomach to begin producing and secreting HCl and pepsinogen, causes a sustained release of gastric juices
Site/smell of food triggers…
-reflex response
-Medulla sends signals to stomach via vagus nerve to gastric
glands to secrete gastric juice (HCl + pepsin + mucus)
-Food arrives in stomach/ distention
-Stretch receptors signal medulla; sends signals via vagus nerve;
causes gastrin secretion from endocrine cells in stomach
-Gastrin causes sustained HCl release (parietal cells) and pepsin
release (chief cells)
HCl activates pepsinogen into ____ in the stomach
pepsin
What are the hormones that inhibit gastrin?
secretin from the small intestine and somatostatin from the hypothalamus
When chyme passes into the small intestine…
duodenum releases the hormones Secretin and CCK to stimulate the pancreas to release pancreatic juices
Pancreatic juices contain…
bicarbonate ions to neutralize stomach acids and pancreatic digestive enzymes
The liver releases bile to…
emulsify fats
Most chemical digestion occurs in the…
small intestine
The pancreas secretes the enzymes:
trypsin, lipase, and amylase
Trypsin breaks down…
proteins into polypeptides
Lipase breaks down…
triglycerides to glycerol and fatty acids
Amylase hydrolyzes…
starch to maltose
How are villi adapted to their function? (MR. SLIM)
-Microvilli = folded to increase surface area for absorption
-Rich capillary network = decrease diffusion distance for
absorption of nutrients and maintain high concentration
gradient for rapid absorption of nutrients
-Single layer of epithelial cells = decreases diffusion
distance
-Lacteals = absorb lipids
-Intestinal glands = release digestive juices/ carrier fluids
-Membrane proteins = facilitated diffusion (large/ polar
molecules; glucose/ amino acids, fructose, vitamins, and
minerals) and active transport (glucose/ amino acids)
What do intestinal crypts do?
release juices that act as carrier fluids for nutrients
Diffusion
Fatty acids easily pass through the hydrophobic cell membranes of the epithelial cells through simple diffusion
Osmosis (in small and large intestine)
Water diffuses across epithelial cell membranes in response to the movement of ions
Facilitated Diffusion
Protein channels within epithelial cell membranes allow passage of hydrophillic food molecules (fructose)
What nutrients are transported via Facilitated diffusion?
water soluble/ polar molecules: fructose, vitamins, glucose, amino acids, and minerals
Active Transport (requires ATP)
Glucose and amino acids are pumped against their concentration gradients or co-transported with Na+ ions as they are actively pumped across the membrane (secondary active transport)
Endocytosis
invagination of the cell membrane to form a vesicle around bulk fluids/ larger molecules that must remain intact in the intestinal lumen and bring them into the cell (ex: antibodies in breast milk)
Pinocytosis
cell drinking
BELCH
Bile Pigments
Epithelial Cells of intestine
Lignin
Cellulose
Human microflora (bacteria)
(Humans do not possess the enzyme cellulase to break down lignin and cellulose)
Cellulose and lignin aren’t digested because…
humans don’t possess enzymes (cellulase) or gut bacteria to break them down
Rate of material movement and fiber content in the intestine are….
positively correlated
Why is fiber important in the diet?
helps clean out damaged intestinal cells and unabsorbed materials, provides bulk to keep materials moving, absorbs water to keep feces moving, works out the body’s microflora, reduces constipation frequency, lowers risk of colon and rectal cancers, lowers blood cholesterol, regulates blood sugar levels by slowing the absorption rate of glucose, decreases hunger to prevent obesity
How does Helicobacter pylori work?
-Secretes urease to neutralize the pH of the stomach and allow its survival, causing infection of the epithelial cell lining
-Secretes mucinase that degrades the mucus lining of the stomach wall
What are the consequences of H. pylori infection?
Stomach ulcers, prolonged exposure for over 20 years may lead to stomach cancers
Treatments of stomach Ulcers
Antibiotics and PPIs (proton pump inhibitors bind irreversibly to proton pumps and prevent H+ secretion, therefore stopping these protons from combining with Cl- ions to form HCl, so the pH of the stomach is raised and the acidity won’t continue to damage ulcers)
What is the function of the teeth and tongue?
Mechanical digestion
What are the functions of the salivary glands?
Moistens food and begins chemical digestion
Amylase is secreted by…
pancreas and salivary glands
What is the function of the Esophagus?
transports food to the stomach
What is the function of the large intestine?
absorbs water and ions, plays a key role in egestion, secretes mucus to lubricate passing feces, aids with the movement of undigested/ indigestible food products through peristalsis
What is the function of the pancreas?
releases digestive enzymes and hormones to neutralize the stomach acid, regulate blood sugar (ex: insulin)
What is the function of the Liver in digestion?
detoxifies blood/ certain molecules, stores vitamins, iron, and glycogen; synthesizes bile
What is the function of the gall bladder?
Stores/ concentrates bile
Trypsin/ endopeptidase is secreted by the…
pancreas
Trypsin is secreted into the ______ which has a _____ pH
small intestine, alkaline
Pepsin/ pepsinogen is secreted by….
chief cells in the stomach
Pepsin/ pepsinogen is secreted into the _____ which has a _____ pH
stomach, acidic
What are proteins broken down into?
amino acids or dipeptides
Starch is a….
carbohydrate
Amylase is secreted into the ____ and ____ which have slightly ____ pH
small intestine, mouth, alkaline
Lipase is released into the _____ which has a slightly ____ pH
small intestine, alkaline
Lipase is secreted by the…
pancreas
Nucleic acids are broken down into ____ by ____
nucleotides, nuclease
Nuclease is secreted by….
pancreas
Nuclease is secreted into the ____ which has a slightly ____ pH
small intestine, alkaline
IB says only “digestion”:
they mean “chemical digestion”
Proton Pumps are found in the….
parietal cells in the gastric pits of the stomach
What are the roles of Proton Pumps?
Maintain acidic conditions in the stomach, actively pump H+ ions into the stomach where they combine with Cl to form HCl
How do PPIs work?
prevent the secretion of H+ ions, thereby preventing the production of HCl which lowers the pH of the stomach
What are the hormones that inhibit gastrin?
secretin from the small intestine andatostatin from the hypothalamus
What is Vibrio Cholerae?
bacterial pathogen that infects the intestines
What are the symptoms of cholera?
Creates diarrhea due to influx of water into the feces, results in dehydration because water is continuously removed from the body’s tissues, can cause death in a matter of hours if not treated through rehydration
How does V. cholerae work?
-releases a toxin that binds to a receptor on the epithelial cells in the intestine
-This activates the ion channels in these cells which are pumped into the intestine.
-Water from the cells follows the ion concentration gradient via osmosis
The liver preforms over 500 functions in the body which is why it has…
an input of blood from two separate sources
HEPATIC ARTERY
delivers oxygen rich blood from the heart to the liver
HEPATIC PORTAL VEIN
delivers nutrient rich blood from the gut to the liver
What are sinusoids?
wide capillaries surrounded by a single layer of hepatocytes
What is the function of sinusoids?
facilitate material exchange between blood and hepatocytes
What occurs in each lobule of the liver?
Smaller branches of the hepatic artery (arteriole)
and hepatic vein (venule) drain into the sinusoids
What is the function of Kupffer cells?
engulf ruptured erythrocytes and their pieces, breaking down the hemoglobin into iron and global which is recycled
When compared to capillaries, sinusoids have…
larger/wider diameter, fenestrations/ openings in the endothelium, and they contain Kupffer cells
Globin
the protein component of hemoglobin
Hyperglycemia
high blood sugar levels
Gastric
having to do with the stomach (such as gastric juices: pepsin and HCl)
Glucose
sugar
Glucagon
Hormone that stimulates hepatocytes to break down glycogen into glucose
Glycogen
stored form of glucose
Glycerol
a product of the breakdown of triglycerides (in addition to fatty acids
Leptin is secreted by cells in the _____ that acts on cells in the _____ to _____
adipose tissue, hypothalamus, suppress/ inhibit appetite
______ cells are damaged with Type 1 Diabetes
Beta
Symptoms of Type 1 Diabetes
high blood sugar, glucose in urine, increased thirst/ urination, hunger, fatigue, weight loss, etc.
If blood glucose levels are high….
-beta cells of pancreas produce insulin
-insulin causes cells to take up/ absorb glucose
-liver stores excess glucose as glycogen
What organ produces hormones to regulate blood glucose levels?
Pancreas
If blood glucose levels are low…
-alpha cells in the pancreas produce glucagon
-glucagon causes the liver to break down glycogen into glucose
-increases glucose levels in the blood
_____ ______ controls the blood glucose levels
Negative feedback
What is bile made up of?
bile salts, cholesterol, bilirubin/ bile pigment
Symptoms/ consequences of Jaundice
yellowing skin, yellowing whites of the eyes, itchiness, pale/ grey feces, darkened urine, brain damage (in infants)
Causes of Jaundice
liver disease (hepatitis, liver cancer, cirrhosis), gall stones, infection, immature liver (newborns)
Excess ____ in the liver is converted into ____
cholesterol, bile salts
What is jaundice?
High/ excess levels of bilirubin which leaks out of the liver into the blood and eventually the bodily tissues
What is the function of peptidases?
breaks down globin of ruptured red blood cells into individual amino acids
Carbohydrate Metabolism
Excess glucose in the blood is stored as glycogen in hepatocytes (controlled by insulin from the pancreas). If blood glucose levels drop, the liver hydrolyzes glycogen into glucose and releases it back into the blood (controlled by glucagon from the pancreas). IF hepatic glycogen stores are depleted, the liver CAN synthesize glucose from other sources (such as fats).
If glycogen stores in the hepatocytes become too low, the liver can…
synthesize glucose from other sources such as fats
Protein metabolism
-Using amino acids from digested proteins, hepatocytes make and secrete plasma proteins
-Hepatocytes also break down the protein component of hemoglobin (globin) into amino acids.
-Amino acids can also be used by the liver to synthesize nonessential amino acids.
-Excess amino acids CANNOT be stored in the body, so the liver breaks them down by removing the amine group (deamination) and converts it into urea (nitrogenous waste removed by the kidneys).
Deamination
Liver breaks down excess amino acids that cannot be stored by removing the amine group and converts it into urea
Lipid Metabolism
-Excess carbohydrates and proteins are converted into fatty acids and triglycerides in the liver.
-Are stored, or used to make cholesterol and phospholipids, which are either stored or transported to other parts of the body by lipoproteins.
-LDL’s take cholesterol TO cells and HDL’s bring cholesterol back to the liver.
-Excess cholesterol in the liver is converted to bile salts, which are used to make bile or egested via the large intestine.
Difference between LDL and HDL
LDL’s carry cholesterol to the cells and HDL’s carry cholesterol back to the liver
What are examples of nutrients stored by the liver?
Glycogen, Vitamin A, Vitamin D, iron, cholesterol, triclycerides
Hepatocytes store and release…
cholesterol, triglycerides, glucose/ glycogen, iron, Vitamin A, Vitamin D
What are some additional functions of hepatocytes?
-Detoxify/ remove harmful substances: alcohol, food preservatives, drugs, poisons, metabolic waste products (urea from deamination)
-synthesize and regulate cholesterol for cell membranes and bile salt production
-produce and secrete bile to emulsify fats
Why does food need to be digested?
-Food molecules that are ingested (taken in/ eaten) are very large (macromolecules), and they are usually insoluble
-must be small enough (in simpler form) to be absorbed – to pass through cell membranes in your digestive tract and into your bloodstream (so you receive “nutrients” – building blocks for your body/ tissues/ cells)
-Certain foods contain materials not suitable for human tissues (these must be separated and removed)
How are proteins digested?
broken down into amino acids or dipeptides first by pepsin (secreted by chief cells in the stomach) in the stomach (acidic pH) and then by trypsin (secreted by the pancreas) in the small intestine (slightly alkaline pH)
How are carbohydrates (starch) digested?
broken down into maltose by amylase (secreted by the salivary glands and the pancreas) in the mouth and small intestine respectively (slightly alkaline pH)
How are lipids digested?
broken down into glycerol and fatty acids by lipase (secreted by the pancreas) in the small intestine (slightly alkaline pH)
What is the role of the stomach in digestion?
-stores and churns food; begins protein digestion
-Protein digestion begins in the stomach
What is the role of proton pumps in the stomach?
-(Found in parietal cells in the gastric pits)
-Maintain acidic conditions of the stomach
-Actively pump protons into the stomach, where they combine with Cl- ions to form HCl
Exocrine Glands
-secrete products through DUCTS to lumen of alimentary canal/ “gut”
-Ducts arise from structures called acini.
-Each acinus is a single layer of secretory cells (held together by tight junctions/ surrounded by a basement membrane); release products (in vesicles) into lumen of duct.
-Secretory cells contain LOTS of ROUGH ER (protein synthesis), Golgi, and Mitochondria (material production/ exocytosis)
Endocrine Glands
Ductless glands that secrete hormones into the bloodstream
What are the causes of Type I Diabetes?
-Early onset
-Beta cells damaged by the body’s own immune system
-autoimmune disease (not enough/no insulin produced)
What are the causes of Type II Diabetes?
-Adult onset
-Insulin receptors on cells are fewer and/or become less sensitive to insulin (decreased body response to insulin)
Symptoms of Type II Diabetes
High blood sugar, glucose in the urine, increased thirst/urination, hunger, fatigue, weight loss, etc.
Treatments of Type II Diabetes
Controlled by managing diet (more fiber/complex carbs/smaller meals/reduce sugar intake = slower/reduced glucose release into blood; less saturated fat = lose weight), and lifestyle
Treatment of Type I Diabtetes
Controlled by insulin injections to regulate blood glucose levels
Sinusoids
-Sinusoids filter the blood and it drains into the hepatic vein back to the heart.
-Sinusoids are small blood vessels that facilitate material exchange between the blood and the hepatocytes.
* Blood drains into each sinusoid through hepatic arterioles (oxygen-rich blood from heart) and hepatic portal venules (nutrient-rich blood from intestine)
* Each sinusoid is lined with a single layer of hepatocytes (one cell layer thick) and contains Kupffer cells
* Sinusoids drain “filtered” blood into a central hepatic vein (which will take clean, deoxygenated blood, under lower pressure, back to the heart)
Blood Flow to the Liver
Blood enters the liver through the hepatic artery and hepatic portal vein and flows into liver capillaries called sinusoids
How does the liver break down and recycle components of erythrocytes?
-Erythrocytes are broken down by phagocytosis.
-Kupffer cells engulf ruptured red blood cells and their “pieces”, and break down their hemoglobin molecules into heme (contains iron) and globin.
-Peptidases break down globin into individual amino acids (used by hepatocytes and other cells to synthesize new proteins or deaminated by the liver)
-Heme groups are broken down into iron
–stored as ferritin in the liver OR transported to the bone marrow to be used in the production of new red blood cells and bilirubin (bile pigment).
Examples of Exocrine Glands
liver, gallbladder, pancreas, salivary glands, intestinal glands, gastric glands
Stomach Acid Overview
-secreted by parietal cells (under control of gastrin) - proton pumps in parietal cells pump H+ ions into lumen of stomach (combines with Cl- to create stomach acid = HCl)
-maintains low/ acidic pH (1.5-2)
-the more H+ ions the lower the pH (and vice versa)
What is the function of villi?
absorption of monomers, vitamins, and minerals from digested food products
________ (hepatic artery branches) and ______ (hepatic portal vein branches) drain into _______ (capillary beds in liver)
Hepatic arterioles, hepatic venules, sinusoids
