Organic Metabolism

A&P Exam 4

Summarize the metabolism that occurs in the absorptive state

Process is anabolic (builds things)

Most energy comes from absorbed glucose

Most excess nutrients are stored as triglycerides

4 fates of glucose in absorptive state

1. Goes to all tissues to provide energy

2. Stored as glycogen in the skeletal muscle

3. Stored in the liver as glycogen

4. Stored in adipose tissues as triglycerides, excess stored here

Fate of triglycerides in absorptive state

Broken down into fatty acids and monoglycerides, stored as triglycerides in adipose tissue

2 fates of amino acids in absorptive state

1. Goes to all tissues and turnt into protein to meet body’s protein demands

2. Excess are taken up by liver, converted into triglycerides and stored in adipose tissue

Summarize the metabolism that occurs in post-absorptive state

Is catabolic (breaks things down)

Most energy comes from stored triglycerides

Ultimately needs to make glucose to send to nervous tissue

Glucose sparing occurs

Ketones derived from fatty acids provide neural energy in prolonged fasts, spares protein catabolism

Define glucose sparing

Most tissues reduce glucose utilization saving it for neural tissue

What ways is glucose made in post-absorptive state

1. Glycogen from the liver

2. Glycogen from muscle (broken down into lactate and pyruvate → lactate in liver)

3. Break down proteins into amino acids in severe fasting states

4. Glycerol from stored triglycerides

What ways are fatty acids made in post-absorptive state

1. Adipose tissue makes fatty acids that go to all other tissues other than nervous

2. Can be turned into ketones to provide energy to neural tissue

   1. Keto diet - lack of carbohydrates so ketones are a stand-in energy source for glucose, but it isn’t the nervous syste'm’s preferred fuel source

What does insulin stimulate in absorptive state

Protein synthesis (amino acids → proteins)

Lipogenesis (glycerol 3-phosphate and fatty acids → triglycerides)

Glycogenesis (glucose → glycogen)

What does a decreased insulin stimulate in postabsorptive state

Proteolysis (proteins → amino acids)

Lipolysis (triglycerides → glycerol and fatty acids)

Glycogenolysis (glycogen → glucose)

Describe paracrine a and b-cells

B-cells secrete insulin (anabolic/net storage, stimulates absorptive rxns)

a-cells secrete glucagon (catabolic/mobilization, stimulates postabsorptive rxns)

What chemical class are insulin and glucagon? Rs, and Rs coupling

Peptides, receptors are on plasma membrane, coupled to secondary messenger signaling cascades

Where are a and b-cells secreted from

Endocrine portion of pancreas called Islets of Langerhans

How does plasma glucose regulate insulin

Increased plasma glucose in absorptive phase → more insulin → more glucose uptake and stopping of glucose output → restoration of plasma glucose to normal

How does insulin operate

Binds to receptor → signal transduction pathway → triggers diffusion of glut-4 vesicles with membrane → uptake of glucose out of the plasma into the ICF where it’s stored as glycogen/fat

Extra notes on insulin operation

Brain doesn’t need insulin for glucose transport (glut-2 transporters exist)

Exercising muscles have glucose transporters go to membrane without insulin

There is a transport maximum

How does type II diabetes affect typical insulin pathway

People have lost sensitivity to insulin. Insulin is present but signal transduction pathway doesn’t occur

Severe - body doesn’t produce insulin

Explain neural controls of fuel metabolsim

Sympathetic → mobilizes fuel, opposes insulin secretion → releases epinephrine → inhibits pancreatic islet beta cells → decrease insulin secretion

Parasympathetic → stores fuel → ACh onto M-AchR → increases pancreatic islet beta cell secretion → increase insulin secretion

How does plasma glucose regulate glucagon

Low plasma glucose in post0absorptive phase → islet alpha cells secrete glucagon → liver has increased glycogenolysis, gluconeogenesis, ketone synthesis → increased plasma glucose and ketones

How does hypoglycemia stimulate glucose mobilization

Low blood glucose → increased glucagon secretion and decreases insulin

Gluconeogenesis needs a baseline level of cortisol (high for anti-insulin effect)

What other factors affect energy

Energy intake affects total-body energy stores

Energy intake affects expenditure (diet, low energy stores → low metabolic rate)

Define leptin

A hormone that is secreted form adipocytes in proportion to the fat they contain, affects BMR

Notes on metabolism

Exercise state is similar to fasted state, needs glucose without food

Why does insulin go down? Sympathetic

Why does muscle glucose uptake stay unaffected? internal glucose transporters

Describe diabetes mellitus (I and II)

Type I - lack of insulin production

Type II - two major pathologies:

• Lack of insulin sensitivity at target cells

• Lack of insulin secretion from beta cells

Describe diabetic ketoacidosis

Occurs with untreated type I diabetes

Affects renal function - increases glucose in filtrate disrupts osmotic gradient

Affects pH balancing - low insulin → high triglyceride breakdown