anatomy midterm 1 - lecture 4 - nutritional physiology i: micronutrients & carbohydrates

what is nutrition?

the process of providing the body with the necessary nutrients for health and growth

what is metabolism?

the sum total of all biochemical reactions within the body

what is anabolism?

• the constructive phase of metabolism

• synthesis of complex molecules from simpler ones

what is catabolism?

• destructive phase of metabolism

• the breakdown of complex molecules into simpler ones

why is hydrolysis important?

• all enzymatic breakdown of food involves hydrolysis

• water molecules are added o bonds between monomers of macromolecules, breaking them down into smaller units

what nutrients?

• the essential building blocks out bodies need to function, grow, and repair

• categorized into macro and micronutrients

what are essential nutrients?

• nutrients that the body cannot produce on its own and must be obtained from the diet

• our bodies cannot function optimally without these essential nutrients, leading to various health problems

what is the function of carbohydrates?

• they are the primary source of energy

• found in grains, fruits, and sugars

what is the function of proteins?

• essential for building and repairing tissues

• found in meat, beans, and dairy products

what is the function of fats?

• important for energy storage, insulation, and hormone production

• found in oils and butter

what is the function of vitamins?

an organic compound that helps regulate bodily processes

what is the function of minerals?

an inorganic element that is essential for various functions

what is the function of water?

essential for hydration, temperature regulation, and nutrient support

what are water-soluble vitamins?

• vitamin C and B vitamins (B2, B3, B5, B6, B7, B9, and B12)

• rapidly absorbed into the bloodstream and is excreted through urine

• must be consumed regularly (no storage)

what are lipid-soluble vitamins?

• vitamin A, D, E, and K

• risk of toxicity

• absorbed along with dietary fats

• doesn’t need to be consumed as frequently as others because they can be stored in fatty tissues or liver for extended periods

what is the main function of vitamin C?

• an antioxidant that donates electrons to neutralize free radicals

• required for collagen synthesis

what is the main function of B vitamins?

they act as coenzymes that support metabolic reactions such as energy production and DNA synthesis

what is the main function of vitamin A?

• it’s converted to retinal for vision

• regulates gene expression in epithelial tissues

what is the main function of vitamin D?

• it acts as a hormone to regulate calcium levels

• essential for bone mineralization

what is the main function of vitamin E?

it’s an antioxidant that embeds in cell membranes and protects them from oxidative damage

what is the main function of vitamin K?

it’s required for activation of clotting proteins and normal blood coagulation

what is the main function of vitamin B12?

• it requires intrinsic factor for absorption in the terminal ileum

• important for myelin maintenance and folate recycling

what is vitamin B1 a precursor for?

thiamine → thiamine pyrophasphate (TPP)

what is vitamin B2 a precursor for?

riboflavin → FAD (coenzyme in the electron transport chain) and FMN

what is vitamin B3 a precursor for?

niacin → NAD+ (coenzyme in many dehydrogenase reactions, accepting hydrogen atoms) and NADP+

what is vitamin B5 a precursor for?

pantothenic acid → coenzyme A (involved in synthesis and oxidation of fatty acids)

what is vitamin B7 a precursor for?

biotin → biocytin

what is vitamin B9 a precursor for?

folate → tetrahydrofolate (THF)

what is vitamin B12 a precursor for?

cobalamin → methylcobalamin and adenosylcobalamin

what must happen for iron absorption to occur?

must be ferrous iron (Fe²⁺) or iron bound to heme

how is dietary iron primarily found?

in the ferric (Fe³⁺) form, which is less readily absorbed

what does gastric acid do in iron homeostasis?

it creates an acidic environment that breaks the bonds between iron and other dietary molecules

what is ferric reductase?

an enzyme on enterocytes that converts ferric iron to ferrous iron, which is more easily absorbed

what happens to ferrous iron after it’s creation?

transported into the enterocytes through a specialized protein DMT1

what happens when iron is inside the enterocyte?

iron may be used locally, stored bound to ferritin, or transported through the bloodstream

how does iron exit the enterocyte?

via ferroportin, which is found on the basolateral surface of an enterocyte to allow it to transport iron into the blood circulation

what happens when iron exits the enterocyte?

• it is oxidized back into ferric (Fe³⁺) by enzymes called ferroxidases

• once oxidized, the iron is immediately bound by transferrin in the blood

what does transferrin do?

it ensures that iron is soluble in the blood and delivers it to tissues throughout the body

where does iron go in the body?

bone marrow (70-80%), muscle (10-15%), and liver (5-10%)

what are RES macrophages?

• specialized immune cells that play a critical role in recycling iron and breaking down aged or damaged RBCs

• RES stands for the reticuloendothelial system

what is hepcidin?

• a hormone that regulates systemic iron levels in the body

• controls how much iron enters the blood by blocking export from cells

• inhibits ferroportin

what happens when hepcidin levels increase?

ferroportin is degraded and iron becomes trapped inside these cells

what causes hepcidin levels to increase?

high plasma levels and inflammation

what causes hepcidin levels to decrease?

blood loss, hypoxia, and increased erythropoiesis

what is a calorie?

the amount of heat energy needed to raise the temperature of water

what are the kcal/g in carbs, proteins, and fats?

4 kcal/g, 4kcal/g, and 9kcal/g

what form of carbohydrate can be absorbed by intestinal cells?

glucose

what is the enzyme responsible for starting carbohydrate digestion in the mouth?

salivary amylase

what does salivary amylase primarily act on?

• starch and glycogen

• breaks large carbs into maltose and short oligosaccharides (does NOT digest)

is there carb digestion in the stomach?

no

what enzyme digests carbs in the small intestine?

pancreatic amylase

what does pancreatic amylase act on?

maltose, maltotriose, and a-limit dextrins

how does the brush border aid in carb absorption?

brush border enzymes are attached to the intestinal cells, so they break down disaccharides and short carb chains into single sugar units (glucose, fructose, and galactose)

what is insulin’s main job?

• help glucose move from the bloodstream into body cells where it can be used for energy or stored

• released after glucose levels in the blood rise

what produces insulin?

beta cells and islets of langerhans

how does insulin lower blood glucose?

by promoting glucose uptake into cells

what is the mechanism of glucose uptake?

1. insulin enters insulin receptor

2. receptor activates signaling cascade through phosphorylation

3. GLUT4 transporters are mobilized

4. GLUT4 is inserted into the cell membrane

5. glucose moves from the blood into the cell

what is phosphorylation?

the addition of phosphate groups to a protein to change its activity

what is the relationship between insulin and GLUT4 transporters?

insulin increases the number of GLUT4 transporters in the membrane

what tissues do not require insulin for glucose uptake?

the brain and liver

what is cellular respiration?

• the process by which cells extract energy from glucose and convert it into ATP

• cells increase this energy gradually

what chemical bonds does glucose have for energy storage?

carbon-hydrogen and carbon-carbon

what is the first stage of cellular respiration?

glycolysis

what is glycolysis?

• a metabolic pathway that breaks one glucose molecule into two molecules of pyruvic acid

• occurs in the cytoplasm, doesn’t require oxygen, and happens in all cells

what are the key outcomes of glycolysis?

2 pyruvic acid, 2 ATP, and high energy electrons captured in NADH

after glycolysis, what pathways could it turn into?

• anaerobic metabolism (fermentation) → no oxygen

• aerobic respiration → oxygen present

what is anaerobic metabolism (fermentation)?

it regenerates NAD+ so glycolysis can continue producing ATP without oxygen

what is aerobic respiration?

cells make ATP by carefully guiding electrons from high energy bonds in glucose to low energy bonds with oxygen

what are the steps of aerobic respiration?

1. pyruvic acid → acetyl-CoA

2. citric acid cycle (krebs cycle)

3. electron transport system (ETS)

what happens to pyruvic acid to become acetyl-CoA?

one carbon atom is removed and is released as CO₂ and NAD+ is turned into NADH

what happens in the citric acid cycle?

• acetyl group in acetyl-CoA is broken down and CO₂ is produced, as well as NADH and FADH₂

• the main purpose is to load electron carriers (NAD and FAD) with high energy electrons, and only a small amount of ATP is produced

what happens in the electron transport system?

• electrons carried by NADH and FADH₂ release energy which is then used to pump protons, creating a proton gradient

• protons then flow through ATP synthase trying to move across the membrane, and that energy produced ATP from ADP and a phosphate

• this is where most ATP is produced

what is glycolysis?

a metabolic process that converts glucose into pyruvate

what is glycogenesis?

• the metabolic pathway that synthesizes glycogen from glucose

• happens when blood glucose levels are high

what is glycogenolysis?

the metabolic pathway that breaks down glycogen into glucose to provide energy or maintain blood glucose levels when glucose is low

what is gluconeogenesis?

the metabolic pathway that synthesizes new glucose from non-carbohydrate precursors, primarily in the liver, to maintain blood glucose levels during fasting or prolonged energy demand

when is insulin released?

when blood glucose is high

how does insulin act in the body vs the liver?

removes glucose vs tells the liver what to do with it (promotes glycogenesis)

how does glucagon help increase blood glucose levels?

it stimulates glycogenolysis in the liver, stimulates lipolysis, and promotes gluconeogenesis

what is amylin?

• a peptide hormone that is co-secreted with insulin by beta cells in response to food intake

• supports insulin’s actions by slowing glucose entry into the blood and reducing further food intake

how does slowed gastric emptying effect the body?

• glucose enters bloodstream more gradually

• smaller and slower increases in blood glucose after eating

what is diabetes mellitus?

a metabolic disease in which blood glucose levels remain abnormally elevated due to problems with insulin secretion, insulin action, or both

what is type 1 diabetes?

• autoimmune (body destroys pancreatic beta cells)

• insulin secretion is deficient or absent

• glucose remains trapped in bloodstream instead of entering cells, leading to high blood glucose levels

what is type 2 diabetes?

insulin is being produced, but the target cells aren’t responding properly, causing insulin resistance