Nutrition, Digestion, Absorption and Homeostasis TEST Flashcards
Causes of PKU (Phenylketonuria)
caused by a person’s chemical inability to metabolize the amino acid phenylalanine into tyrosine
Phenylalanine builds up in tissues & bloodstream due to lack of enzyme (phenylalanine hydroxylase) that breaks phenylalanine down into tyrosine, from inheriting mutated form of gene
Why do foods need to be digested?
Food molecules that are ingested are very large, and they are usually insoluble
Macromolecules must be broken down so that they are small enough to be absorbed so an individual can receive nutrients – building blocks for your
body/ tissues/ cells)
Additionally, certain foods contain materials not suitable for human tissues (egestion)
4 major organic molecules/macromolecules
Proteins
Carbohydrates
Lipids
Nucleotides
Proteins - monomers broken down into, specific enzymes that break them down, where each enzyme is secreted, location of optimal pH for enzyme
Enzyme: Pepsin/endopetidase/protease
Gastric glands into stomach - acidic (proteins to peptides)
Pancreas into lumen of small intestine - neutral/slightly alkaline (proteins/peptides to amino acids)
Carbohydrates - monomers broken down into, specific enzymes that break them down, where each enzyme is secreted, location of optimal pH for enzyme
Enzyme: Amylase (small intestine and salivary)
Starch to maltose
7 pH in mouth
7-8 pH in small intestine
Lipids - monomers broken down into, specific enzymes that break them down, where each enzyme is secreted, location of optimal pH for enzyme
Lipase
Pancreas into lumen of small intestine
7-8 pH
Triglycerides to Monoglycerides/fatty acids/glycerol
Nucleotides - monomers broken down into, specific enzymes that break them down, where each enzyme is secreted, location of optimal pH for enzyme
Nuclease
Pancreas to small intestine
7-8 pH
Nucleic acids to nucleosides
Roles of HCl and proton pumps in the stomach
Proton pumps pump H+ ions into the stomach, allowing for the production of hydrochloric acid. HCl accelerates digestion, activates enzymes such as pepsin and gives optimal pH for digestion.
Roles of PPIs in the reduction of stomach acid and ulcers
PPI’s (proton pump inhibitors) bind irreversibly to proton pumps and prevent H+ secretion, raising pH of stomach (may make people more susceptible to gastric infection though)
Hormonal and nervous mechanisms that control the secretion, content and volume of gastric juice. Role of vagus nerve!
- Site/ smell of food triggers reflex response – brain (medulla) sends impulses (via vagus nerve) to gastric glands in stomach to secrete gastric juice (pepsin,HCl)
- Food enters stomach causing distention – detected by stretch receptors in stomach lining
- Impulses from stretch receptors sent to medulla oblongata which sends signal to stomach through vagus nerve that triggers gastrin secretion into bloodstream, and causes stomach to begin producing and secreting HCl (parietal cells) and pepsinogen (chief cells)
- Gastrin causes sustained release of gastric juices
- If pH becomes too low (< 1.5-2.0), gastrin inhibited by hormones (secretin from the small intestine/ somatostatin from the hypothalamus)
- Once digested food (chyme) passes into small intestine, duodenum releases hormones secretin and CCK (cholecystokinin) to stimulate pancreas to release pancreatic juices (bicarbonate ions to neutralize stomach acids and pancreatic digestive enzymes) and liver to release bile (emulsify fats)
Which cells in the gastric pits secrete which components of gastric juice?
Parietal Cells - HCl
Chief Cells - Pepsin
Role of the pancreas in digestion
Names of enzymes it secretes
Specific food molecule/substrate each enzyme acts on, molecules produced by the reaction
Digestive enzymes are primarily produced and secreted by the pancreas (outside of salivary glands (salivary amylase) and the stomach (pepsin)).
Enzymes are secreted by the pancreas through a duct into the lumen of the small intestine (exocrine gland)
Each enzyme acts on a specific substrate
Note: Secretin (hormone from small intestine) stimulates the pancreas the release enzymes and bicarbonate ions as chyme passes into small intestine from stomach. Bicarbonate ions neutralize stomach acid and provide optimum pH for digestive enzymes in small intestine
General function of villi
How the structure of a villus is adapted to its function
Identify structures of a villus
State function of each villus structure that it helps to carry out
Each villus (singular) is surrounded by a single layer of epithelial cells (decreases distance nutrients must diffuse to be absorbed into bloodstream)
Each epithelial cell contains an outer layer
of folded projections called microvilli
Within each epithelial cell are many mitochondria and pinocytotic vesicles
Pinocytotic vesicles translocate digested food products (fluids) in bulk
Tight junctions in epithelial cells form an impermeable barrier between the plasma membranes of
adjacent epithelial cells, ensuring a one-way flow of food materials and ensuring that
digestive fluids and body-tissue fluids remain separate at all times!
Within each villus is a rich
capillary network:
minimize diffusion distance, maintain large concentration gradient for rapid absorption
Within each villus is a lacteal that absorbs lipids
Between each villus are cells called intestinal crypts that release juices that act as “carrier fluids” for nutrients
Diffusion - which nutrients, when, etc///
Fatty acids and other small,
non-polar substances
easily pass through the
hydrophobic cell
membranes of
epithelial cells through simple diffusion
Facilitated Diffusion - which nutrients, when, etc///
Protein channels within epithelial cell membranes (of villi and microvilli) allow passage of hydrophilic food molecules (water-soluble/ polar molecules like fructose, vitamins, glucose, amino acids, and minerals)
Active Transport - which nutrients, when, etc///
Glucose and amino acids are pumped (membrane proteins) against their concentration gradients, or they are transported with Na+ ions (co-transport) as Na+ ions are actively pumped across the membrane (secondary active transport)
Endocytosis - which nutrients, when, etc///
Invagination of the cell membrane to form a vesicle around bulk fluids/ large molecules that must remain intact in the intestinal lumen and bring them into the cell (pinocytosis: “cell drinking”)
(breastmilk)
Role of the large Intestine
MAIN FUNCTION: Absorption of water (and minerals/ vitamins/ ions)
Highly folded – maximizes surface area for absorption of water into the blood
Secretes mucus
Lubricates passing faeces
Movement of indigestible food products
Peristalsis
Egestion
BELCH
Bile pigments
Epithelial cells
Lignin
Cellulose
Human microflora/bacteria
Role of fiber in the diet
Rate of movement through the intestine is positively correlated with fiber content
helps “clean out” old/ damaged intestinal cells and unabsorbed materials, it provides bulk to keep materials moving, it absorbs water to keep faeces soft and easy to pass, “works out” the body’s normal microflora, reduces frequency of constipation, lowers risk of colon and rectal cancers, lowers blood cholesterol, regulates blood sugar levels
How cholera can cause dehydration
V. cholerae releases a toxin that binds to a receptor on the epithelial cells in the intestine.
This activates ion channels in these cells so that ions (including chloride ions/ Cl-) are pumped out of these
cells and into the intestine.
Water from the cells follows the
ion concentration gradient (by
osmosis).
Excess water dilutes feces =
diarrhea, and will cause
dehydration (if left untreated) as
water is continuously removed
from body tissues
Causes/consequences/treatments for stomach ulcers
- H. pylori survives the
acidic conditions of
stomach by penetrating
mucus lining (mucosa):
Secretes urease to increase pH and to
neutralize gastric acids to allow survival, and
attachment to and infection of epithelial
cells lining stomach wall (underneath
mucus lining) - Causes inflammation (body’s immune response) which damages goblet cells in stomach lining (secrete mucus) and H. pylori also secretes mucinase which degrades the mucous lining of stomach wall. As mucus breaks down, stomach wall/ epithelial lining damaged/ digested by stomach acid/ HCl and pepsin (ulcers) - treated with antibiotics and PPI’s
Prolonged damage to stomach wall (and chronic H. pylori infection = 20+ years) may lead to stomach cancers
Dual blood supply to the liver
Why?
Outline circulation of blood through sinusoids of the liver
Because the liver is the largest gland in the body and it performs over 500 different vital
functions, it has a unique input of blood from two separate sources.
The hepatic artery (branches off
aorta) delivers oxygen-rich blood
from the heart to the liver (for
liver cells to use)
The hepatic portal vein delivers nutrient-rich blood from the gut (from the capillaries of the
villi in the intestines) to the liver (blood from pancreas/ spleen/ stomach/ colon too)
Blood enters sinusoids (capillary network on the liver)
Blood enters the liver through the hepatic artery and hepatic portal vein and flows into liver
capillaries called sinusoids.
Sinusoids are wide blood vessels (capillaries) surrounded by a single layer of
hepatocytes (liver cells)
Sinusoids filter, detoxify, and balance levels of nutrients in the blood (removing excess
nutrients to be stored in the liver, removing toxins, and adding nutrients (stored in the
liver) to the blood when needed) - prevents osmotic imbalance in blood
Sinusoids also engulf and break down “old”/ damaged erythrocytes (red blood cells).
OUtline structure and function of liver sinusoids and know the function of each part
The liver is made up of smaller structures called lobules (star-shaped/ hexagonal structures). In each lobule, smaller branches of the hepatic artery (hepatic arterioles) and smaller branches of the hepatic portal vein (hepatic venules) drain into liver capillaries called sinusoids. Sinusoids filter the blood and it drains into the hepatic vein (back to heart).
Role of liver in the regulation of nutrient levels in the blood
Nutrients stored in the liver (also broken down, recycled, released)
Receives, processes, and stores nutrients from the absorbed from the intestines to balance nutrient levels in the blood
Hepatocytes (liver cells) store and release: cholesterol, triglycerides, glucose/ glycogen, iron, vitamin A, and vitamin D
Helps to regulate blood sugar levels (hepatocytes store excess glucose as glycogen - under control of insulin; glycogen hydrolyzed to glucose when blood sugar levels low - under control of glucagon)
Detoxifies blood (hepatocytes detoxify/ remove harmful substances - alcohol, food preservatives, drugs, poisons, metabolic waste products
How are erythrocytes broken down and how are their components recycled?
Broken down by kupffer cells into the heme portion and the globin portion. Heme broken down into iron and bilirubin and the iron can be transported to bone marrow to create more red blood cells.
Roles of hepatocytes in sinusoids
To facilitate the exchange of a wide variety of substances between the blood and hepatocytes,the hepatocytes are directly exposed to the blood passing though the organ, by being in close contact with the liver blood sinusoids.
Production of bile and its components by the liver
Excess cholesterol in the liver is converted to bile salts, which make bile.
Causes/consequences of jaundice
Bilirubin leaks into the blood - yellow skin
Causes: Liver disease (hepatitis, liver cancer, cirrhosis), gall bladder obstruction/ blocked bile duct/ gall stones, increased RBC damage (anemia), infection (parasite), immature liver (in newborns)
Consequences: yellowing skin, yellowing sclera (whites of eyes), itchiness, pale/ grey feces, darkened urine, brain damage (in infants)
How is the pancreas able to act as an endocrine gland to regulate blood glucose levels (VERY SPECIFIC).
The pancreas produces hormones that control the levels of glucose.
If glucose levels in the blood are high, beta-cells produce insulin, which causes the cells to take up and absorb glucose. The liver stores excess glucose as glycogen.
If glucose levels are low, alpha cells produce glucagon. Glucagon causes the liver to break down glycogen into glucose. Glucagon increases levels of glucose in the blood.
Negative feedback controls the glucose levels.
Effect of glucagon and insulin on hepatocytes, muscle cells and other cells.
Glucagon and insulin affect cellular respiration rates to affect the ability of the cell to convert glycogen into glucose (more cellular respiration = more glycogen-glucose conversion)
Causes, symptoms and treatments of TYPE I DIABETES
Early onset
Beta cells damaged/ destroyed by body’s own immune system – autoimmune disease (not enough/ no insulin produced)
Triggered by various factors (illness etc.) – not usually genetic
Controlled by insulin injections to regulate blood glucose levels
Symptoms: high blood sugar, glucose in urine, increased thirst/ urination, hunger, fatigue, weight loss etc.
Causes, symptoms and treatments of TYPE II DIABETES
Adult onset
Insulin receptors on cells (liver, muscles etc) are fewer and/ or become less sensitive to insulin (decreased body response to insulin)
Related to obesity, poor diet, genetic history, lack of exercise, age, ethnicity
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
Symptoms: high blood sugar, glucose in urine, increased thirst/ urination, hunger, fatigue, weight loss etc.
Where is leptin secreted?
ADIPOSE TISSUE!!!!!!!
Glycogen
Polymer of glucose. When there is excess glucose, it is stored as GLYCOGEN.
Glycerol
component of monoglyceride (fatty acid chain + glycerol)
Glucagon
Produced by ALPHA cells when glucose is too low. Stimulates the breakdown of glycogen into glucose to raise blood sugar.
Glucose
Main type of sugar in the blood. Converted from glycogen.
Gastrin
Hormone which produces HCl and Pepsin
Gastric
Describes the juices in the stomach which
Glycemic
Relates to levels of blood sugar (hyper high, hypo low)
Globin
part of hemoglobin (a protein) - used to synthesize non essential amino acids
Esophagus function
moves food down from mouth to stomach. amylase working
Stomach function
acidic environment for protein denaturation, harmful pathogens to be killed
Stores and churns food
Liver Function
Detoxifies certain molecules
Stores vitamins, iron, glycogen,
Synthesizes bile
Small intestine function
Absorption of nutrients
Salivary Glands function
Moistens food into a bolus
Begins polysaccharide digestion
Gall Bladder function
Stores/concentrates bile
Osmosis
Water diffuses across epithelial cell membranes in response to movement of
ions and other hydrophilic monomers (occurs in small intestine and large intestine)
