DAT Biology: Endocrine System

Hormones

Chemical messengers throughout the body, coordinating activity between cells, tissues, and organs

Endocrine Signaling

Hormones secreted directly into the bloodsream, eventually landing at receptors of another cell

Paracrine Signaling

Hormones secreted to neighboring cells

Autocrine Signaling

Hormones secreted onto the same cell which is secreting it

Peptide Hormones

Protein-based hormones made of polypeptides

Created in the rough ER by linking amino acids together via peptide bonds

Ligand-Gated Receptors

Receptor proteins capable of inducing intracellular signal transduction pathways once an extracellular lignad is bound

Second Messengers

Signaling molecules independent of the og hormone which propagate signals within the cell (intracellular effect from outside)

Includes cAMP, IP3, DAG, and Ca2+

GPCRs

Ligand-Gated Receptor, G Coupled Protein Receptors, associated witht he G protein on the intracellular domain

Responsible for conveying intracellular signals

Example: IP3/DAG pathway

Receptor Tyrosine Kinases (RTKs)

Ligand-Gated Receptor

Two mirror components twin/dimerize once a peptide hormone is bound

Intracellular RTK domains cross-phosphorylate to kick a second messenger response—RTK components phosphorylate each other to influence intracellular signals

Ligand-Gated Ion Channels

Channel proteins which change shape once a ligand is bound in order to allow the flow of ions across membranes

IP3/DAG Pathway

Regulates the release of stored Ca2+ from the endoplasmic reticulum into the cell cytosol

Steroid Hormones

Hormones made from modified cholesterol molecules in the smooth ER

Basic fused 4-ring structure with differentiating functional groups

Example: All hormones produced by the adrenal cortex and gonads — adrenal cortex: glucocortioids, mineralcorticoids, androgenic steroids, reproductive organs: progesterone, testosterone, estrogen

Amino Acid Derived Hormones

Median of steroid and peptide hormones; smaller than peptide hormones as they are mainly derived from a singular amino acid tyrosine

Depending on the specific amine, they can act like a water-soluble peptide hormone on cell surfaces or lipid-soluble steroid hormone inside the cell

Produced in the rough ER and cytosol

Represent all hormones of the adrenal medulla (epinephrine, norepinephrine) and T3 and 4 hormones

Hypothalamus

Responsible for regulation of hormone secretion in the body, coordinating the body’s internal environment and maintaining homeostasis

Pituitary Gland (Hypophysis)

Crucial gland for hormone production, storage, and release

Rests just below the hypothalamus, and contains the anterior pituitary and the posterior pituitary

Posterior Pituitary Gland (Neurohypophysis)

Direct neuronal extension of the hypothalamus constructed of neuronal tissue

Stores and releases hormones produced by the hypothalamus, in th eform of ADH (antidiuretic hormone) and oxytocin

Antiduretic Hormone (ADH)

Vasopressin

Increases water reabsorption in the nephron by increasing the number of aquaporins in the collecting duct

Reabsorption of water into the blood, and antiduretic (decrease in urination)

Oxytocin

Causes uterine contraction during child labor and the release of milk during breastfeeding, targeting the uterus and mammary glands

In positive feedback loop

Plays a role in facilitating “maternal behavior”

Anterior Pituitary (Adenohypophysis)

Produces its own hormones and is composed of glandular tissue rather than neural tissue

Releases 6 major hormones controlling growth, stress, and reproduction

Once stimulated, the anterior pituitary can release its own hormones

Hypothalamic Releasing Hormones

Hormones released by hypothalamus in order to stimulate the release of hormones generated by the anterior pituitary gland

Hypothalamic Inhibiting Hormones

Hormones released by the hypothalamus to inhibit the release of other hormones by the anterior pituitary

Hypopohyseal Portal System

Connects the anterior pituitary gland to the hypothalamus and allows for quick diffusion of hormones through a portal vein

GnRH (Gonadotropin Releasing Hormone)

Causes the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH)

TRH (Thyrotropin Releasing Hormone)

Causes the release of thyroid stimulating hormone (TSH)

CRH (Corticotropin Releasing Hormone)

Causes the release of adrenocorticotropic hormone (ACTH)

GRH (Growht Hormone Releasing Hormone)

Causes the release of growth hormone (GH)

Tropic Hormones

Targets other endocrine glands for further hormone release

Direct Hormones

Directly targets organs to cause effects

Anterior Pituitary Gland Hormones

Hormones released by the anterior pituitary gland once stimulated

FSH (Follicle Stimulating Hormone)

Anterior Pituitary Gland Tropic Hormone

Responsible for follicle growth in female ovaries for increased production of estrogen and progesterone and sperm maturation in male gonads by stimulating steroli cells

LH (Luteinizing Hormone)

Stimulates ovulation (estrogen and progesterone) when a surge of it is present during menstruation, the formation of the corpus lutem in females, and the production of testosterone in male gonads

ACTH (Adrenocorticotropic Hormone)

Stimulates the release of glucocorticoids from the adrenal gland to fight stress, increasing the body’s glucose levels

TSH (Thyroid Stimulating Hormone)

Stimulates the thyroid gland to produce T3 and T4 in order to increase metabolism

Prolactin

Stimulates the development of the mammary gland and increases milk production following childbirth

Growth Hormone (Somatotropin)

Stimulates the growth and division of body cells

Pineal Gland

Gland in the brain responsible for the production of melatonin, hormone involved in regulating the circadian rhythm

Thyroid Gland

The largest of the endocrine organs, it is in front of the trachea

Parathyroid Glands

Endocrine glands on the posterior side of the thyroid gland

Thyroid Gland Hormones

T3 T4 Calcitonin

T3

Type of thyroid gland hormone, Triiodothyronine

Active form of the hormone set, 4x more potent than T4

T4

Type of thyroid gland hormone, Thyroxine

Stable form of the hormone due to additional iodine atoms

Calcitonin

Decreases blood calcium levels upon release from the parafollicular thyroid cells (C cells)

Stimulates osteoblast use of calcium to generate new bone, inhibits osteoclasts from freeing calcium by breaking down bone, decreases calcium reabsorption in the kidneys and intestines

Hypothyroidism

The result of undersecretion of T3 and T4, causing reduced basal metabolic rates, reducing metabolism overall

Oversecretion of TRH to compensate for missing T3 and T4, enlarged thyroid gland

Basal Metabolic Rate (BMR)

Minimum number of calories your body needs to stay alive while at rest

Hyperthyroidism

Result of oversecretion of T3 and T4, causing increased basal metabolic rates, faster metabolism

Hyperactive + Enlarged Thyroid Gland

Goiter

Caused by both hyperthyroidism and hypothyroidism

Irregular, physical enlargement of the thyroid gland

Iodine Deficinecy

Leading cause of goiters (components of T3 and T4)

Parathyroid Hormone

Increases blood calcium levels in the blood, opposite of calcitonin

• Stimulates osteoclasts to free calcium by breaking down bone

• Inhibits osteoblast use of calcium to generate new bone

• Increases calcium reabsorption in the kidneys and intestines

Pancreas

Endocrine gland consisting of endocrine and exocrine tissues

Endocrine Cells

Secrete hormones directly into the bloodstream to act on different part of the body

Exocrine Cell

Secrete hormones into ducts to a body surface

Endocrine (Islets of Langerhans)

Secretion of the peptide hormones glucagon, insulin, and somatostatin

Pancreatic Exocrine

Secretion of digestive enzymes into the small intestine via the pancreatic duct

Glucagon

Released by alpha cells in times of low blood glucose

Stimulates liver and adipose fat tissues to release stored glucose

Insulin

Peptide hormone released by beta cells in times of high blood glucose, associated with the RTK

Stimulating the liver and adipose fat and muscle tissues to store glucose

Somatostatin

Inhibitory hormone from the pancreatic delta cells responsible for inhibiting the release of insulin from the beta cells, glucagon from the alpha cells, and growth hormone from the anterior pituitary

Adrenal Glands

Two types: adrenal cortex (outer region) and adrenal medulla (inner region) associated with stress combatting

Adrenal Cortex

Outer region of the adrenal gland, combats longer term stress

Releases steroid hormones upon stimulation by ACTH from the anterior pituitary gland

Adrenal Medulla

Inner region of the adrenal gland, combats short term stress

Releases amino acid-derived hormones in response to stimulation by the sympathetic nervous system

Glucocorticoids (Cortisol)

Steroid hormone released by adrenal cortex, raises blood glucose levels for fuel use during long periods of stress, lowers immune response as a tradeoff

Mineralocorticoids (Aldosterone)

Steroid hormone released by adrenal cortex, inc reases blood volume and blood pressure by increasing reabsorption of Na+, and therefore passive reabsorption of water via osmosis

Androgens

Small amounts produced by the adrenal cortex, male sex hormones produced in small amounts by the adrenal cortex

Catecholamines

Produced by the adrenal medulla; Fight or Flight Hormones; Epinephrine and Norepinephrine, binds to adrenergic receptors

Increases heart rate and breaks down glycogen into glucose

Epinephrine

Produced by the adrenal medulla; Binds alpha and beta adrenergic receptors to cause vasoconstriction and vasodilation

Vasoconstriction occurs with alpha receptors

Vasodilation occurs with beta receptors

Long Term Stress

Addressed by adrenal cortex

Examples: prolonged, insufficient access to food and water

Addressed with steroid hormones

Short Term Stress

Addressed by the adrenal medulla

Examples: sudden, frightening event or a perceived immediate threat to health and safety

Addressed with amino acid derived hormones

Cortisol

Body’s main stress hormone made by adrenal glands

Manages stress, controls blood sugar, reduces inflammation, and regulates blood pressure

Positive Feedback Loop

Product increases the production of the stimulus, generates exponential growth

Example: contractions due to oxytocin during labor

Negative Feedback Loops

Product inhibits the production of the stimulus, generates homeostasis