ANSC 300 - Ch. 6 - Endocrinology

Biochemical communication

Secreted signals

Electrical communication

Ion flow

Direct contact communication

Gap junctions or cell surface proteins

Juxtacrine

Next to each other

Ex: gap junctions and cell adhesion molecules

Autocrine

Cell sends signal to itself

Paracrine

Cell send signals to cells nearby

Endocrine

Transports through the blood

Ex: Hormones

Exocrine

Goes outside the body

Ex: Pheromones

Homeostasis

Goal is to maintain stability over time

Regulatory mechanisms are required

Stimulatory and Inhibitory Mechanisms

Cells sometimes have both

Signals must be integrated

Stronger signal wins out

Homeorhesis

Changes parameters over time

Regulatory mechanisms alter trajectory and magnitude of change

Ex: Growth, lactation, aging, pregnancy

What is the best example of molecular complementarity?

Antibody-antigen interaction

GPCR

Seven transmembrane G-protein coupled receptors

Peptide and amino acid derivatives

Polypeptides (insulin, growth hormone)

Small peptides (GnRH, oxytocin)

Dipeptides (thyroid hormone)

Single amino acid (catecholamines)

Cholesterol derivatives (steroids)

Adrenal and gonadal steroids

Vitamin D

Fatty acids

Prostaglandins and Prostacyclins

Ions

Calcium

Endocrinology

Study of the production, regulation and action of hormones produced from endocrine glands

Hormone

Term coined over 100 years ago by Starling and Bayliss in conjunction with their landmark study on secretin production by the small intestine

Examples of endocrine glands

Hypothalamus

Pituitary

Pineal

Thyroid

Parathyroid

Pancreas

Adrenal

Ovaries

Testes

Examples of endocrine tissues

Adipose

Heart

Placenta

Kidney

Liver

Hypothalamus endocrine functions

Growth hormone - skeletal growth

ADH - water balance

Reproductive endocrine systems

Ovaries and Testes

Pulsatile secretion

Occurs in the hypothalamus and pituitary

Diurnal secretion pattern

Occurs with GH and melatonin

Cyclical secretion pattern

Occurs only in females

Episodic secretion pattern

Occurs with insulin and epinephrine

Specificity endocrine signaling

Expression of receptors by a cell confers the ability to respond to specific hormones

Sensitivity endocrine signaling

Determined by the number and “activity” of hormone receptors

Measured in terms of a response to the hormone

Neuroendocrinology

Study of the relationship between the nervous and endocrine systems

Hypothalamus structure and function

Structure: Small area of the brain; organized into nuclei

Function: produces releasing hormones; subject to regulation by higher brain centers

Pituitary gland

Directly regulated by the hypothalamus

Pineal gland

Entrains hormone secretion to light/dark cycle

Portal Circulation

Closed system

RHs usually released in primary plexus (median eminence)

Capillary fenestrations (leaky) promote RH uptake

Capillary fenestrations in secondary plexus promote RH release into AP

Acidophil

Somatotroph (GH) and mammotrophs (prolactin)

Basophil

Corticotrophs (ACTH), gonadotrophs (LH/FSH) and thyrotrophs (TSH)

What are the benefits of the hypothalamic-pituitary portal system?

Faster communication between hypothalamus and pituitary

Less hypothalamic hormone is needed to elicit response in pituitary,

Better responsiveness to changing physiological conditions

POMC-derived hormones

ACTH, LPH, MSH, beta-endorphin

ACTH actions

Stress adaptation; stimulates cortisol and aldosterone secretion from adrenal gland

LPH actions

Stimulates lipolysis in adipocytes

MSH actions

Stimulates melanin synthesis and reduce food intake

Beta-endorphin actions

Endogenous opioid; decreases pain sensors; stimulates PRL and GH and inhibits GnRH release

Cushing’s Disease

Disease that involves excessive cortisol secretion

Involves fat redistribution to the face and neck

Includes fragile skin (tearing, bruising)

Includes high BP, glucose, fatigue, and thirst

Glycoprotein hormones

TSH, LH, FSH, and hCG

TSH actions

Stimulates release of thyroxin (T4) and triiodothyronine (T3)

FSH action

Follicle growth + sperm production

LH actions

Progesterone and testosterone production; Pregnancy

hCG actions

Maternal recognition of pregnancy

Somatomammotropic hormones

GH and PRL

GH actions

Bone and muscle growth; fat and sugar metabolism; anabolic which causes nitrogen retention and increased muscle mass

PRL actions

Mammary development and lactation; reproduction; growth; stress

Posterior pituitary hormones

Oxytocin and Vasopressin

Oxytocin actions

Milk letdown and parturition

Vasopressin actions

Water reabsorption; blood pressure; glycoprotein breakdown; memory and learning

What hormones stimulate maternal behavior?

Prolactin and Oxytocin

Describe how pup retrieval behavior is assessed?

Observing the amount of time it takes the mother to retrieve displaced pups

Monogamy Model

Monogamous in the wild (socially and sexually)

Coparent young

Pair bond formation

24 hours of contact

Breeding contact

Pair bond establishment

Increased affiliative behavior towards mate

Increased aggression towards strangers

Agonist

Partner preference formed after 6 hours (no estrus or breeding behavior)

Antagonist

Failure to form pair bond after 24 hours of exposure while in estrus

Traumatic Brain Injury

Most common cause of death in young adults

Can result from repeated head trauma

Causes high incidence of chronic hypothalamic and/or pituitary dysfunction

Which hormones are part of a larger pro-protein?

ACTH, oxytocin, ADH

Qualities of endocrine diseases

Hormone overproduction/deficiency

Tumors

Often mimic other diseases

Slow to develop

Treatment depends on cause of disease

Grave’s Disease

Swelling and enlargement of the extraocular muscles behind the eye cause the eyeball to “pop” forward

Acromegaly

Unregulated growth hormone release

PCOS

Multiple non-ovulatory follicles

High androgen production

Insulin resistance

Obesity

Negative Feedback

Major regulatory mechanism for regulating hormone production

Allows for fine control of cellular responses

Changes depending on stage of cycle