Endocrine System: Hormone Classification, Regulation, and Action

Melatonin Classification

amino acid derivative (tryptophan)/ second messenger (Gi)

Melatonin Regulation

Circadian control via light signals from optic nerve traveling to the suprachiamatic nuclei (SCN) to inhibit release - levels increase as light decreases; developmental controls

Melatonin Action

involved in setting sleep patterns acts to relax somatic muscle tone; acts in signaling sexual maturation in some animal models but that has yet to be clearly defined in humans

T3 and T4 Classification

amino acid derivative (tyrosine)/ direct, transcription factor

T3 and T4 Regulation

negative feedback loop involving TSH; hormones are produced as part of thyroglobulin in the colloid of the follicle; hormones are cleaved off thyroglobulin prior to release

T3 and T4 Action

increases production of glycolytic enzymes; stimulates ATP production; promotes ATPase production and action (calorigenic effect); increases heart rate(chronotropic) and contractibility(inotropic); T3 is stronger with a 24 hour ½ life, T4 has a 7 day ½ life

Calcitonin Classification

peptide/second messenger majority Gs, some Gq

Calcitonin Regulation

negative feedback loop in response to increased serum calcium levels

Calcitonin Action

brings calcium levels down; inhibits osteoclast activity; promotes excretion of calcium in kidney by decreasing calcium permeability in the loop of Henle; in children, stimulates osteoblast activity

Parathyroid Hormone (PTH) Classification

peptide/second messenger majority Gs, some Gq

Parathyroid Hormone (PTH) Regulation

negative feedback loop in response to decreased serum calcium levels

Parathyroid Hormone (PTH) Action

brings calcium levels up; inhibits osteoblast activity; increases production of osteoclasts; increases calcium permeability and reabsorption in the loop of Henle; stimulates the release of calcitriol from kidney; increases calcium absorption in intestines

Thymosins Classification

peptide/second messenger Gq

Thymosins Regulation

stimulated by prolactin; stimulated by interleukins released in response to infection and inflammation; inhibited by steroid hormones (especially stress hormones)

Thymosins Action

promotes stem cell mitosis and T-cell differentiation in bone marrow; regulates T-cell maturation in thymus

ANP and BNP Classification

peptide/second messenger G-protein, increases cGMP

ANP and BNP Regulation

ANP releases in response to distension of atrial cells; BNP released in response to stretch receptors in ventricles; secretion of both is enhanced by high sodium concentration.

ANP and BNP Action

decreases sodium and pressure; promotes vasodilation; increases glomerular filtration rate in kidney; decreases kidney permeability to sodium and water increasing excretion of both; suppresses thirst and taste bud salt sensitivity; inhibits aldosterone, renin, and ADH release; stimulates lipolysis

Aldosterone Classification

steroid/direct, transcription factor

Aldosterone Regulation

negative feedback loop in response to increased K+, decreased Na+, and/or decreased blood volume or pressure; release is also stimulated by Angiotensin II

Aldosterone Action

increases sodium and blood pressure/volume; increases permeability in the kidney distal and collecting tubules by stimulating the production of Na+ pumps; increases both Na+ and water (due to Na+ movement) reabsorption; enhances ADH; stimulates taste bud sensitivity to salt.

Cortisol Classification

steroid/direct, transcription factor

Cortisol Regulation

negative feedback loop involving ACTH; diurnal (circadian) release, highest in morning; stimulated in response to stress

Cortisol Action

increases blood sugar; promotes protein catabolism and amino acid release from cells; stimulates amino acid uptake and gluconeogenesis in liver; inhibits glucose uptake in muscles and adipose; stimulates lipolysis; suppresses inflammation and immune response

DHEA Classification

steroid/direct, transcription factor

DHEA Regulation

small amounts released in response to ACTH; converted to testosterone in the testes and adipose tissue

DHEA Action

not significant; action is overshadowed by gonadal hormones; promotes bone and muscle growth in children; no effect in adult males; majority converted to estrogens in women; promotes blood cell production and muscle maintenance in women.

Epinephrine (adrenaline) & Norepinephrine (noradrenaline) Classification

amino acid derivative (tyrosine)

Epinephrine & Norepinephrine Regulation

direct stimulation by sympathetic nervous system in response to stress

Erythropoietin (EPO) Classification

glycoprotein/ G-protein, increases GTP

Erythropoietin (EPO) Regulation

negative feedback loop, released in response to decreased oxygen levels in the blood

Erythropoietin (EPO) Action

promotes the production of erythrocytes in bone marrow

Renin Classification

peptide/ none - enzyme used to initiate the renin-angiotensin system

Renin Regulation

negative feedback loop, released in response to decreased Na+ levels or blood volume; inhibited by ANP & BNP

Renin Action

converts a serum protein, angiotensinogen to angiotensin I

Angiotensinogen Classification

peptide/ inactive form

Somatomedin c (IGF-1) Classification

peptide/ second messenger, tyrosine kinase

Somatomedin c (IGF-1) Regulation

release is stimulated by GH

Angiotensin II Classification

glycoprotein/ second messenger Gq

Angiotensin II Action

promotes vasoconstriction; stimulates the release of aldosterone; indirectly enhances ADH

Glucagon Classification

peptide/ second messenger Gs & Gq

Glucagon Action

stimulates glycogenolysis in liver and skeletal muscle; promotes gluconeogenesis in the liver and lipolysis in adipose tissue

Insulin Classification

peptide/ tyrosine kinase coupled to PIP2

Insulin Action

increases glucose transporter activity (primarily in the liver); promotes conversion of glucose to glycogen; stimulates glycolysis; increases protein synthesis; increases fatty acid uptake and triacylgycerol production in adipose

Somatostatin (GHIH) Classification

peptide/ second messenger varied, Gs, Gq, and G-protein/K+channels

Pancreatic Polypeptide Classification

peptide/ second messenger Gs

Pancreatic Polypeptide Action

satiation; decreases appetite; plays a role in moderating food intake

Ghrelin

produced in the stomach; stimulates GH and hunger

Gastrin

produced in the stomach in response to food intake; stimulates acid production, mucous lining, and pancreas acini

Motilin

secreted by the small intestine during fasting to maintain basic motility

Cholecystokinin (CCK)

secreted by duodenum in response to filling; stimulates pancreatic acinar and gallbladder secretions into duodenum

Secretin

produced by the duodenum in response to acid; stimulates the release of water and bicarbonate from pancreas and gallbladder

Gastric Inhibitory Polypeptide (GIP)

released from small intestine in response to high fat and sugar content in food; slows motility and stimulates insulin release

Estrogen Classification

steroid/ direct, transcription factor

Inhibin (Ovaries) Action

negative feedback with FSH; inhibits FSH and additional follicle development

Progestin (progesterone) Action

stimulates development of the uterine endometrial lining; works with prolactin to stimulate mammary glands for lactation

Testosterone (androgen) Action

promotes sperm maturation; stimulates calcium absorption, muscle and bone growth; regulates the development of secondary sex characteristics

What are the primary physiological functions of blood?

Transportation of dissolved substances, defense against infection, pH regulation, fluid balance, thermoregulation, and clotting.

What is the difference between plasma and serum?

Serum is plasma from which the clotting factors have been removed.

What is the primary function of albumin in the blood?

It maintains oncotic pressure and assists in the transport of various substances.

Where does initial hematopoiesis occur during embryonic development?

In islands of the extraembryonic yolk sac membrane during late gastrulation.

Which organ serves as the primary site of hematopoiesis during early to mid-gestation?

The fetal liver.

When does the bone marrow become the primary site of hematopoiesis?

At birth.

What happens to the bone marrow in the diaphysis as a person ages from 4-5 years old?

Adipose tissue infiltrates the marrow cavity, replacing the hematopoietic tissue.

In an adult, where is hematopoietic marrow primarily located?

In flat bones, vertebrae, and the epiphyses of the humerus and femur.

What hormone directs the maturation of proerythroblasts?

Erythropoietin (EPO).

Why do reticulocytes decrease their expression of fibronectin receptors?

To facilitate their release from the marrow stroma into the circulation.

What is the functional advantage of the biconcave shape of an erythrocyte?

It provides an increased surface area-to-volume ratio for efficient gas exchange.

How does the erythrocyte cytoskeleton allow the cell to withstand shear force?

It forms a shell that allows the membrane to slide around the inner cytoplasmic contents like a tank tread.

What is the composition of a hemoglobin molecule?

Four subunits, each consisting of a polypeptide chain (2 alpha and 2 beta) and a heme group containing a central Fe2+ ion.

What is the effect of carbon monoxide on hemoglobin?

It binds irreversibly to hemoglobin, significantly lowering the cell's oxygen-carrying capacity.

What does the sigmoidal shape of the hemoglobin dissociation curve indicate?

It indicates cooperative binding, where the affinity for oxygen increases as more oxygen molecules bind to the hemoglobin.

What physiological effect occurs when the hemoglobin dissociation curve shifts to the right?

The affinity for oxygen decreases, causing hemoglobin to release more oxygen to the tissues.

Why does fetal hemoglobin have a higher affinity for oxygen than adult hemoglobin?

Fetal hemoglobin contains gamma chains instead of beta chains, which do not interact with 2,3-DPG, shifting the curve to the left.

What is the role of carbonic anhydrase in the erythrocyte?

It converts CO2 and water into carbonic acid, which then dissociates into bicarbonate and H+ ions.

What is the function of the band 3 protein in the erythrocyte membrane?

It acts as an anion exchanger, moving bicarbonate out of the cell in exchange for chloride ions.

Where are aged erythrocytes primarily removed from circulation?

By macrophages in the spleen, liver, and bone marrow.

What happens to the iron salvaged from broken-down erythrocytes?

It is transported by transferrin to the bone marrow for new cell production or to the liver for storage.

What is the byproduct of the breakdown of the heme porphyrin ring?

It is converted into biliverdin and subsequently into bilirubin.

How is bilirubin eliminated from the body?

It is excreted via bile into the GI tract, where microbial activity converts it into urobilinogen and stercobilins for excretion.

What is the significance of 2,3-DPG in blood storage?

A decline in 2,3-DPG levels limits the storage life of blood in blood banks by affecting the oxygen dissociation curve.

What is the primary significance of the ABO blood system in transfusions?

It refers to the specific groups of antigens presented on the erythrocyte cell surface.

What is the genetic basis for the O blood phenotype?

It results from a mutation that prevents the glycosylation of the H antigen.

Why is the Rh factor clinically significant during pregnancy?

It is tested to identify potential immune responses by the mother against the fetus.

How do leukocytes change morphology when moving from blood to tissue?

They transition from a spherical shape in blood plasma to an amoeboid shape in tissue.

What cytokine triggers the differentiation of myeloid precursor cells into granulocytes or monocytes?

Granulocyte-monocyte colony stimulating factor (GM-CSF).

Which leukocyte type is typically the first to respond to infection or injury?

Neutrophils.

How do neutrophils kill bacteria after engulfing them?

They fuse granules and lysosomes with the phagosome to lower pH and release enzymes, while lactoferrin binds iron to deprive bacteria of nutrients.

What is the composition of pus?

It consists of apoptotic neutrophils, bacteria, cell debris, and extracellular fluid.

Which leukocytes are primarily responsible for modulating inflammatory responses and fighting parasites?

Eosinophils.

What effect do corticosteroids have on eosinophil counts?

They cause a decrease in eosinophil numbers.

Which leukocyte type mediates inflammation by releasing histamine and heparin?

Basophils.

What is the relationship between basophils and mast cells?

They share a common progenitor and are nearly identical, though they have slightly different development pathways.

Into what cell types do monocytes mature after infiltrating tissues?

Macrophages in connective tissue, microglia in the CNS, and osteoclasts in bone.

What is the primary function of T lymphocytes?

They protect against foreign cells that present specific markers or antigens.

Which type of lymphocyte is responsible for the surveillance of abnormal or cancerous cells?

NK (natural killer) cells.

From which giant cell do thrombocytes (platelets) originate?

Megakaryocytes.

What are the three stages of hemostasis?

Vascular stage, platelet stage, and coagulation.

What is the function of von Willebrand's factor during the platelet stage of hemostasis?

It promotes the binding of platelets to the damaged surface, making the surface 'sticky' to facilitate adhesion.

What is the role of ADP released by adhered platelets?

It attracts more platelets to the site, promoting platelet aggregation.