Midterm 3 - Lecture 17 Flashcards
What is metabolism?
A set of chemical reactions that modifies a molecule into another for storage, or for immediate use in another reaction or as a byproduct
- anabolism = build up
- catabolism = break down
6 metabolic hormones
- insulin
- glucagon
- growth hormone (somatotropin)
- thyroid hormones (T3, T4, thyroxine)
- cortisol (broadly, glucocorticoids)
- epinephrine (or adrenaline)
What is the metabolic response to hormones dependent on?
concentration and exposure duration
What are the 4 hormone classes?
- peptide and protein
- amino acid derivatives
- thyroid hormones and catecholamines - fatty acid compounds
- steroid
- confined to adrenal cortex, sex glands, and placenta
2 pancreatic hormones
insulin and glucagon
What cells of the pancreas produce insulin and glucagon? What are these regions known as?
- region: islets of Langerhans
- b-cell: insulin
- a-cell: glucagon
When are insulin levels high?
when plasma glucose levels are high
How does the hypothalamus and pituitary gland work?
- hypothalamic-pituitary portal system transports neurohormones from hypothalamus to the anterior pituitary
- hypothalamic neurohormones bind to receptors on endocrine cells in the anterior pituitary
- regulate hormonal secretion
What is the central link between CNS and the endocrine system?
hypothalamic-pituitary portal system
- allows high concentration of hormone without being diluted in the systemic circulation
What is the ‘Master Gland’?
anterior pituitary
What are the hormones of the ‘master gland’?
- follicle-stimulating hormone
- luteinizing hormone
- growth hormone aka somatotropin
- thyroid stimulating hormone
- adrenocorticotropic hormone (ACTH)
- prolactin
What are tropic hormones?
hormones that regulate secretion of other hormones
- ex. anterior pituitary hormones
What are the common glucocorticoids in mammals vs birds and rodents?
mammals = cortisol
birds and rodents = corticosterone
Does cortisol have a negative feedback effect?
Yes
- negative feedback in pituitary (stops ACTH production) and hypothalamus (stops ACTHRH production)
What are glucocorticoids essential for?
Essential for promotion of gluconeogenesis and lipolysis in starvation
- transcription of genes necessary for these processes requires presence of glucocorticoids
- increases blood glucose by stimulating gluconeogenesis and inhibiting glucose uptake (anti-insulin)
What would happen if an animal had no glucocorticoids?
no glucocorticoids = no living due to hypoglycemia
Circadian rhythm
ACTH and cortisol highest early in the morning and lowest in the evening
What is a glucocorticoid deficiency disease?
Addison’s Disease
- dogs
- autoimmune disease destroying adrenal cortex
- dizziness from reduced blood pressure
- inappetant and weak
- depressed, dehydrated, and vomit
- ACTH produced in excess (no cortisol for negative feedback)
What is a glucocorticoid overproduction disease?
Cushing’s Disease
- dogs, cats, horses
- excessive ACTH
- eat and drink more, lose hair, thin skin, weak muscles
- anti-insulin effect of glucocorticoids leads to diabetes mellitus in some patients
What is epinephrine a potent inducer of?
- glycogenolysis
- most important during stress
- secondary means to increase blood glucose availability during exercise
What are the 2 adrenergic receptors?
- Alpha-adrenergic receptors
- Beta-adrenergic receptors
Alpha-adrenergic receptors
- increases calcium in target cells and stimulates their activity
- same affinity for epinephrine and norepinephrine
Beta-adrenergic receptors
- Beta 1
- found in heart
- increase HR and SV - Beta 2
- found in heart, liver and skeletal muscle
- inhibitory
- induce hyperglycemia and glycogenolysis in liver
- increased breakdown of triglycerides in adipose
- increased HR
Where is growth hormone produced? What does it stimulate?
- in anterior pituitary and stimulates growth of body mass and elongation of bones
- expression regulated by stimulatory and inhibitory mediators from hypothalamus, GHRH and GHIH
- GH production also affected by plasma nutrient concentrations (glucose, FFA, AA)
- stimulated by sex hormones during puberty
What increases the release of growth hormone?
- strenuous physical activity
- starvation
- stress
- low plasma glucose
What cells produce insulin-like growth factor 1 (IGF-1)?
Produced by many cells, but mostly in liver in response to GH release
- primary mechanism GH stimulates growth
What does insulin-like growth factor 1 stimulate?
Stimulates cell growth and proliferation in almost every cell of the body
- muscle, bone, liver, kidney, nerves, skin, lungs, hematopoietic
Does GH stimulate IGF-1 secretion in underfed animals?
no
Where is the thyroid gland located?
2 lobes located on either side of the trachea
What are characteristics of the thyroid gland?
- hollow spheres of interspersed with capillaries
- colloid (center of sphere) is where synthesis occurs and is stored)
- C-cells produce calcitonin
- PTH produced by spherical cluster of parathyroid cells
- Calcitonin and PTH regulate calcium concentration
Where are calcitonin and PTH synthesized?
Thyroid gland
- C-cells produce calcitonin
- cluster of parathyroid cells produce parathyroid hormone
What does calcitonin and PTH regulate?
calcium concentration
What are the two thyroid hormones?
- T3 and T4
- 3 and 4 refer to # of iodide atoms
- T4 and T3 circulate bound to proteins
How is the thyroid regulated?
Thyroid stimulating hormone (TSH) is a glycoprotein secreted by thyrotropes
- feedback controlled by T3 and T4
- TSH acts on thyroid gland to stimulate synthesis and secretion of T4
TSH also increases number and size of follicular cells
- prolonged increase results in hyperplasia and hypertrophy = goiter
What are the actions of T3 and T4
- increase metabolic rate in all tissues except brain, gonads and spleen resulting in increased O2 consumption and heat production
- acts by binding nuclear receptors on DNA
- induce expression of genes - increases secretion if prolonged cold exposure
- increased metabolic rate to stay warm
How are T3 and T4 synthesized?
- iodide taken up by active transport
- iodide oxidized by thyroperoxidase (TPO)
- T4 and T3 formed by iodination of thyronine - during secretion small colloid-containing vesicles are taken up by follicular cells from follicular lumen
- thyroid hormones are released from thyroglobulin by lysosomal enzymes
- free hormones diffuse out of cells
- transported throughout body bound to thryoid-binding globulin
*T4 is converted to T3 in the liver bc T3 is more potent
Hyperthyroidism
- excessive production of thyroid hormone
- elevated HR, wt loss, increased appetite
Hypothyroidism
- most common endocrine disease in dogs
- reduced thyroid hormones results in reduced GH secretion and reduced heat production
- animal = sluggish, reluctant to move, overwt, and appetite reduced
- can be induced by inadequate iodine intake
How does insulin effect the liver, muscle and apdipose?
LIVER
- increase glycogen synthesis and glycolysis
- decrease glycogenolysis, gluconeogenesis, ketogenesis
MUSCLE
- increase glucose and AA uptake
- decrease proteolysis
ADIPOSE
- increase glucose and FFA uptake
- decrease lipolysis
How does glucagon effect the liver, muscles, and adipose?
LIVER
- increase glycogenolysis, gluconeogenesis, ketogenesis
MUSCLE
- minimal action
ADIPOSE
- increase lipolysis
How does cortisol effect liver, muscles, and adipose?
LIVER
- increase glycogenolysis, gluconeogenesis
MUSCLE
- decrease AA uptake and insulin action
- increase proteolysis
ADIPOSE
- increase lipolysis
- decrease insulin action
How does growth hormone effect liver, muscles, and adipose?
LIVER
- increase gluconeogenesis, IGFs/IGFBP
MUSCLE
- increase AA uptake
- decrease glucose uptake
ADIPOSE
- increase lipolysis
- decrease glucose uptake
How does epinephrine effect liver, muscles, and adipose?
LIVER
- increase glycogenolysis, gluconeogenesis, ketogenesis
MUSCLE
- increase glycogenolysis
- decrease insulin action
ADIPOSE
- increase lipolysis
- decrease insulin action
