Untitled Quiz

Female Physiology & Reproductive Hormones

• Reproduction is controlled by the nervous and endocrine systems.
• The hypothalamus is the neural control center for reproductive hormones.
• Neural regulation occurs through simple neural reflexes and neuro-endocrine reflexes (neurohumeral reflexes).

A-Neural (Nervous) Regulation

• Simple neural reflexes: Neurotransmitters are released directly onto target tissues, such as for ejaculation (glans penis) or temperature-sensitive neurons in the scrotum.
• Neuro-endocrine reflexes (neurohumeral reflexes): Neurohormones (released by neuro-secretory cells) enter the bloodstream and act on target tissues, such as the suckling reflex or ovulatory reflex.

Hormonal Signaling

• Chemical signals (hormones) are secreted into body fluids (usually blood) to communicate regulatory messages within the body.
• Endocrine action: Hormones travel long distances via the bloodstream to target cells.
• Paracrine action: Hormones act locally by diffusing to nearby cells.
• Autocrine action: Hormones act on the same cell that produced them.
• Direct signaling across gap junctions: These water-filled channels allow small signaling molecules to diffuse between neighboring cells.

Neurocrine Action (Synaptic Signaling)

• Neurotransmitters diffuse across small distances between nerve cells (synapses).
• Neurotransmitters are chemical messengers that are released from the cell body a long distance from the target.

Neurotransmitters vs. Hormones

• Neurotransmitters: Released by nerve cells and travel across synapses. Faster action, shorter duration. Part of the nervous system.
• Hormones: Released by endocrine glands and travel through the bloodstream to distant target cells. Slower action, longer duration. Part of the endocrine system.

Hormones: Chemical signaling mechanisms

• Hormones are classified based on the distance they travel to their target cells; endocrine, paracrine, & autocrine hormones.
• Solinocrine communication releases hormones directly into the lumen of the reproductive tract.

Pheromones

• These are secreted to the outside of the body, generally volatile, and detected by members of the same species olfactory system (and perhaps the vomeronasal organ.
• Examples of types of chemical signaling include; endocrine, paracrine, & neuronal

Major Types of Intercellular Signaling

• Juxtacrine signaling: Gap junctions or ligand-receptor interaction on cell surfaces.
• Endocrine signaling: Ligands (hormones) secreted into the blood for long-distance transport to target receptors.
• Paracrine signaling: Secretion of ligands diffused locally to bind to target cells.
• Synaptic signaling: Axon terminus secretes ligands (neurotransmitters) into a restricted environment to target cells like nerves or muscle and chemical messenger.

Mode of Hormonal Actions

• Alternate target tissue metabolism.
• Stimulate or depress secretory or synthetic activities of target organs.
• Don't directly change gene structure; activate or inhibit gene expression.

Reproductive Hormones Classified by Origin & Mode of Action

• Origin: Hypothalamus, pituitary, gonads, uterus, placenta.
• Mode of action: Release of other hormones, stimulate gonads (gonadotropins), sexual promotion (steroids), pregnancy maintenance, and luteolysis.
• Biochemical classification: Peptides, glycoproteins, steroids, prostaglandins.

Classification by Glandular Origin

• Hypothalamic hormones: GnRH, dopamine, CRH, growth hormone-releasing hormone, etc.
• Pituitary hormones: FSH, LH, prolactin, ACTH, oxytocin, etc.
• Gonadal hormones: Ovary hormones (E2, inhibin, oxytocin, P4, relaxin, etc.), Testis hormones (androgens, inhibin, estrogen, etc.)
• Uterine & placental hormones: Prostaglandins F2 alpha (PGF2α), progesterone, estrogens, relaxin, equine chorionic gonadotropin (eCG), and human chorionic gonadotropin (hCG), etc.
• Other glands: Pineal gland, Liver, and Adrenal gland.

Hormones Classified by Mode of Action

• Neurohormones: Synthesized by hypothalamic neurons, stored/released by posterior pituitary (oxytocin).
• Releasing Hormones: Ex. GnRH, which controls FSH and LH release from the anterior pituitary.
• Gonadotropins: Synthesized/secreted by specialized cells in the anterior pituitary (FSH, LH).

Sexual Promoters (steroids) - Pregnancy Maintenance - Metabolic Hormones

• Secreted by gonads, regulate hypothalamus and anterior lobe of pituitary; Examples: Estrogen, progesterone, testosterone
• hormones involved in pregnancy maintenance, such as P4 (progesterone) and placental lactogen.
• Metabolic hormones, like thyroid hormone (thyroxine) and growth hormone, influence metabolism.
• Adrenal corticoids, produced by the adrenal cortex, govern stress response.

Biological Action of Hormones by Chemical Structure

• Glycoproteins: Polypeptide + carbohydrate. Bound to membrane receptors.
• Steroids: Contain cholesterol nucleus. Binds to nuclear receptors.
• Peptides: Small molecules; joined by peptide bonds.

Mechanism of Action of Protein Hormones

• Hormone diffuses from blood and binds to membrane receptor specific to hormone.
• Receptor-hormone complex activates G-protein, which activates the enzyme adenylate cyclase.
• Adenylate cyclase converts ATP to cAMP (second messenger)..
• cAMP activates protein kinases in the cytoplasm.
• Protein kinases activates specific enzymes that alter cellular activities

Mechanism of Action of Steroid Hormones

• Diffuse across the plasma membrane of the target cells.
• Combine with receptor proteins in the cytoplasm or nucleus.
• Hormone-receptor complex enters the nucleus and triggers gene transcription (initiation of mRNA synthesis for new proteins).
• mRNA leaves nucleus and attaches to ribosomes, directs the synthesis of new proteins.

Characteristics of Reproductive Hormones

• Act in minute quantities (nanograms or picograms per mL of blood).
• Have relatively short half-lives.
• Bind to specific receptors to initiate intracellular biochemical reactions .
• Displays feedback regulation.

Hormone Patterns of Secretion

• Episodic (fast): Secreted in short bursts, often under nervous control. Example: Oxytocin.
• Basal (tonic): Low, steady levels, fluctuates with small pulses, usually under hypothalamic control. Example: GnRH.
• Sustained: High levels for a prolonged period. Examples: High progesterone during pregnancy maintenance.
• Circadian: Related to the light-dark cycle, example: melatonin.

Hormone Oxytocin

• A 9 amino acid peptide, neuropeptide.
• Secretion from the posterior lobe of the pituitary.
• Effects: Milk let-down, uterine contractions, including myometrial contraction (parturition), induction of foaling, and sperm/oocyte transport, induction, or other functions.
• Uses: inducing parturition, enhancing uterine clearance, treating milk letdown difficulties.
• Pharmacokinetics: Typically administered parenterally; response occurs quickly after IV administration, and 3-5 minutes after IM.

Contra-indications of Oxytocin Use

• Known hypersensitivity to oxytocin.
• Dystocia due to abnormal fetal presentation requires correction before oxytocin administration

Hormone TRH (Thyrotropin-releasing hormone)

• A tripeptide hormone that regulate thyrotrophic hormone from pituitary gland, TSH; stimulating lactotropes from pituitary gland to release prolactin.
• Uses: Treatment of agalactia and diagnostic tests for thyroid gland disorders.

Hormone GnRH (Gonadotropin-releasing hormone)

• Decapeptide hormone from the hypothalamus.
• Stimulates FSH and LH release from the anterior pituitary.
• Important for ovulation and other reproductive processes.

GnRH Agonists & Antagonists

• Analogs and agonists initiate pituitary release of gonadotropins (FSH & LH).
• Antagonists interfere with GnRH action.

Biological Activity for hormone GnRH

• Regulates the release of FSH and LH to induce ovulation in mares.
• Use in estrous synchronization protocols, cystic ovarian disease treatments, embryo transfer programs, and induction of postpartum ovulation, or treatment, or other uses in reproductive processes.

Hormonal Classification by Biochemical Structure

• Glycoproteins: FSH, LH, etc. (contain carbohydrate)
• Steroids: Estrogen, progesterone, testosterone, etc. (derived from cholesterol)
• Peptides: GnRH, oxytocin, TRH, etc- (short chain amino acids)
• Prostaglandins: PGF2α, etc (lipids)
• Other categories: Includes insulin-like growth factors (IGFs).

Mechanism of Action for Protein & Steroid hormones

• Protein hormones act via cell membrane receptors.
• Steroid hormones act through nuclear receptors regulating gene transcription.

Hormone Follicle Stimulating Hormone (FSH)

• Glycoprotein hormone.
• Essential for follicle development.
• Promotes estrogen production and follicular maturation, leading to ovulation.
• Involved in spermatogenesis.
• Clinically useful for stimulating puberty in heifers, superovulation in dairy cows, treatment of ovarian inactivity, and other reproductive processes.
• Can control the expression of several different genes in various reproductive tissues.

Hormone Luteinizing Hormone (LH)

• Polypeptide, heterodimeric glycoprotein.
• Vital for ovulation, luteinization, and androgen/estrogen production.
• Stimulates androgen production in males.
• Crucial for ovulation in females and development & maintenance of the corpus luteum during early pregnancy (luteotropic effect)
• Clinically useful for ovulation, treating cystic ovarian disease, and other reproductive processes.

Hormone Human Chorionic Gonadotropin (hCG)

• Glycoprotein with a high concentration of LH and lower concentration of FSH.
• Used in clinical treatments for inducing ovulation and other processes.

Hormone Inhibin

• Glycoprotein, part of transforming growth factor family.
• Involved in the negative feedback regulation of FSH secretion in both males and females.

Hormone Activin

• Member of TGF family.
• Impacts FSH biosynthesis and secretion.
• Important to the development & function of several tissues, in certain processes like folliculogenesis and other actions in the ovary.

Hormone Corticotropin-releasing hormone (CRH) & Adreno-cortico-tropic hormone (ACTH)

• CRH(peptide H, 41 a.a) from paraventricular nucleus of hypothalamus; synthetized by placenta with duration of pregnancy.
• ACTH (peptide H, 35 a.a.) from corticotropes of anterior pituitary gland that response for CRH stimulation
• Regulation of stress response, fetal development, and other functions

Hormone Cortisol (Glucocorticoids)

• Steroid hormone.
• Important for normal fetal development, production of surfactants, myelin, retinal, pancreatitis, and mammary development.
• Used clinically to induce parturition and in cases of allergies and inflammation.

Hormone Aldosterone

• Regulates concentration of Na, K in blood.
• Reabsorption/secretion of ions in the kidney.
• Helps to maintain electrolyte balance and blood pressure.

Hormone Cortisone

• Hormone of the adrenal cortex that has a complex effect on glucose, fat, and metabolism.
• Used to treat or manage various problems/diseases.

Adrenal Medulla Hormones (Adrenalin)

• Includes dexamethasone and betamethasone.
• Synthetic corticosteroids to induce abortion or parturition.

Hormone Prolactin (LTH)

• Polypeptide (199 amino acids), secreted by lactotrophs (mammotrophs) in the anterior pituitary.
• High values in pregnant and lactating animals.
• Normal values are generally below 25-30 ng/ml.
• Aids in maintaining the corpus luteum (luteotropic activity) in some species; also associated with milk production and other maternal behaviors like nest building, feeding behavior, or caring for young..

Antiprolactins (Dopamine agonists)

• Useful for inducing estrus or termination of pregnancy; treat pseudo-pregnancy.
• Examples include bromocriptine, cabergoline, and metergoline.
• Their action is due to their abilities to reduce or block prolactin, which affects other processes in the body.

Hormone Relaxin

• Polypeptide similar to the structure of insulin & IGF (insulin-like growth factors); secreted by the placenta in mares and by other tissues, such as the ovary (CL) or prostate gland in males.
• Activities include reducing collagen content in the extracellular matrix, inhibiting uterine contractions, and assisting with mammary gland development.

Hormone Insulin-like growth factors (IGF)

• Polypeptides similar to insulin.
• Modulate fetal/placental growth, puberty, steroidogenesis.
• Plays diverse roles during animal development.

Hormone FSH (Follicle-stimulating hormone)

• Glycoprotein; comprised of α & β-subunits, and crucial in follicle growth and development, including the synthesis of estrogen (E2), an essential process for follicle maturation and ovulation.

Hormone PMSG (Pregnant Mare Serum Gonadotropin)

• Glycoprotein hormone produced by the placenta of pregnant mares.
• Valuable as a source of FSH and clinically used for superovulation or for stimulating puberty in females.

Hormone LH (Luteinizing hormone)

• Glycoprotein hormone with a critical role in ovulation in females.
• Stimulates the production of a variety of hormones, such as progesterone and a variety of other important sex hormones, including those related to male reproduction.
• Supports theca internal function, leading to the production of steroid hormones with various biological functions and roles in the reproductive process.

Hormones activities during the final stage of follicle development, ovulation

• They can trigger cell responses associated with histamine formation, endometrium preparation for implantation, granulosa cell stimulation.
• It may stimulate theca cells; ovulation (release of an egg) will occur in time due to hormone's role & action on certain reproductive tissues.

Progesterone's role(P4) in pregnancy and related functions

• Responsible for maintaining pregnancy and influencing other reproductive processes
• Plays a key role in preparing the uterus for implantation.
• Important in regulating progesterone levels to maintain uterine lining.

Prostaglandins (PGs)

• Lipid-derived hormones; plays a role in uterine motility, ovulation, luteolysis (breakdown of the corpus luteum).
• Commonly used to induce uterine contractions and luteolysis.
• Involved in numerous reproductive processes, including inducing estrus, inducing parturition, or regulating other components in the reproductive response.
• Uses include uterine evacuation, regulating estrus cycles, mediating parturition and other similar activities in several species.

Melatonin

• Synthesized in the pineal gland; functions as a key regulator of circadian rhythms.
• Associated with the regulation of the light-dark cycle and seasonal reproduction.
• Plays roles in various reproductive and behavioral processes or conditions.

Other Reproductive Hormones

• Includes melatonin, testosterone, pregnant mare serum gonadotropin (PMSG), human chorionic gonadotropin (hCG), follistatin, bradykinin, and placental lactogen.
• Varies by species and context, exhibiting a range of effects on different reproductive stages.

Commercial Preparations for Estrogen

• Oral tablets, transdermal preparations, ointments.
• Useful for treating various equine and other animal reproductive conditions; a key hormone for various effects related to the sexual or reproductive system.

Commercial Preparations for Progesterone

• Oral tablets, injectable forms, or intravaginal devices (CIDRs).
• Used in treating or preventing pseudo-pregnancy, ovulation, or other issues with reproduction.

Commercial Preparations for Prostaglandins

• Injectable forms.
• Used clinically for inducing parturition, managing metritis, or synchronizing estrous cycles.

Commercial Preparations for Hormones (Various)

• Various forms for managing and treating a range of conditions from induced ovulation to treatment of cystic ovarian disease in different species by administration.
• Many include various forms suited to particular delivery strategies (oral, injected, topical).