Endocrine System and Hormones

• Communication and coordination are processes governed by the nervous and endocrine systems.
• The nervous system uses neurotransmitters for communication.
• The endocrine system relies on hormones.
• Hormones are chemical messengers traveling in the bloodstream to reach tissues and organs.
• Tissues, cells, and glands secrete hormones.

Exocrine vs. Endocrine Glands

• Exocrine glands secrete substances onto epithelial surfaces via ducts.
• Endocrine glands secrete hormones directly into the bloodstream.

Feedback Loops

• Negative feedback is a mechanism where the response counteracts the initial change.
• Positive feedback reinforces the initial change, amplifying the response.

Major Organs of the Endocrine System

• Pituitary gland
• Adrenal gland
• Thyroid gland
• Parathyroid gland
• Pancreas
• Pineal gland
• Thymus
• Gonads

Secondary Organs of the Endocrine System

• Skin
• Heart
• Gastrointestinal tract
• Kidneys
• Liver
• Placenta
• Adipose tissue

Pituitary Gland

• The pituitary gland sits in the sella turcica.
• It connects to the hypothalamus via the infundibulum.
• The posterior pituitary stores and secretes hormones from the hypothalamus: antidiuretic hormone and oxytocin.
• The anterior pituitary is regulated by the hypothalamus.
• There are 6 other hormones produced by the anterior pituitary.

Posterior Pituitary: Antidiuretic Hormone (ADH)

• ADH originates from the supraoptic nuclei of the hypothalamus.
• It travels to they hypothalamus via the hypophyseal tract.
• Target tissue is the kidney.
• ADH promotes water retention, decreasing urine volume and raising blood pressure.
• ADH secretion is stimulated by low blood pressure and certain drugs/substances.

Antidiuretic Hormone Regulation - Drugs

• Nicotine, morphine and barbiturates stimulate ADH secretion.
• Alcohol inhibits ADH secretion.

Posterior Pituitary: Oxytocin

• Oxytocin originates in the paraventricular nucleus of the hypothalamus.
• It is carried by the hypothalamo-hypophyseal tract.
• Oxytocin's major target tissues are the uterus and breast.
• It is a very important chemcial messenger in the brain.

Oxytocin Regulation

• Stretch receptors in the uterus and cervix stimulate oxytocin release.
• Infant nursing can also trigger oxytocin release.

Oxytocin Effect

• Contraction of uterine muscles.
• Is involved in "letdown" reflex in lactation.
• Plays a role in sexual arousal and orgasm.
• Is known as the "cuddle hormone" due to its role in affectionate behavior.

Anterior Pituitary

• The anterior pituitary is composed of glandular tissue.
• It produces and secretes its own hormones.
• It produces tropins or tropic hormones.
• Stimulated by the hypothalamus.
• Receives regulatory hormones through the hypothalamo-hypophyseal portal system.

Anterior Pituitary Hormones

• Growth hormone (GH)
• Adrenocorticotropic hormone (ACTH)
• Thyroid stimulating hormone (TSH)
• Gonadotropins
  • Follicle stimulating hormone (FSH)
  • Luteinizing hormone (LH)
• Prolactin (PRL)
• Regulated by hypothalamic releasing and inhibiting hormones.

Hypothalamic Releasing and Inhibiting Hormones

• Growth hormone-releasing hormone (GHRH)
• Corticotropin-releasing hormone (CRH)
• Thyrotropin-releasing hormone (TRH)
• Gonadotropin-releasing hormone (GnRH)
• Prolactin-inhibiting hormone (PIH)
• Somatostatin (aka Growth hormone-inhibiting hormone (GHIH))

Anterior Pituitary Hormone: Growth Hormone (GH)

• GH's target tissue is all cells, but it has the most drastic effect is on bone and skeletal muscle.
• It originates from somatrope cells.
• GH increases cell size, cell division, muscle mass, and long bone growth.

Growth Hormone Regulating Hormones

• Growth hormone-releasing hormone (GHRH) stimulates growth hormone release.
  • It induces the liver to produce insulin growth stimulants and insulin-like growth factor (IGF-1).
• Somatostatin (or GHIH) inhibits GH production.
  • It is produced in response to increasing GH levels.

Growth Hormone Abnormalities

• Decreased GH leads to pituitary dwarfism.
• Increased GH leads to acromegaly.

Anterior Pituitary: Adrenocorticotropic Hormone

• ACTH originates from corticotrope cells.
• It targets the adrenal cortex.
• ACTH causes the production of glucocorticoids.

Adrenocorticotropic Regulating Hormones

• Corticotropin-releasing hormone (CRH).
• Rising levels of glucocorticoids cause inhibition of the pityitary through decreasing CRH.

Anterior Pituitary: Thyroid Stimulating Hormone (TSH)

• TSH originates from thyrotrope cells.
• It targets the thyroid.
• TSH increases production and release of thyroid hormone.

Thyroid Stimulating Hormone (TSH) Regulating Hormone

• Thyrotropin-releasing hormone (TRH).
• Elevated levels of thyroid hormone inhibit the production of:
  • TRH by hypothalamus.
  • TSH by anterior pituitary gland.

Anterior Pituitary: Gonadotropins

• Follicle-stimulating hormone (FSH) stimulates gamete production.
• Luteinizing hormone (LH) stimulates hormone production.
• They originate from gonadotrope cells.
• Target tissues are:
  • ovaries
  • testis

Gonadotropins Regulating Hormones

• Gonadotropin-releasing hormone (GnRH).
• Produced by the hypothalamus in response to gonadal hormones.

Anterior Pituitary: Prolactin

• Prolactin Origin - lactotropes
• Target Tissue - breasts
  • Stimulates milk production

Prolactin Regulating Hormones

• Thyrotropin-releasing hormone (TRH)
• Prolactin-inhibiting hormone (PIH)
• Prolactin-releasing hormone (PRH) - MAYBE?

Prolactin Regulation - Female

• PRL levels rise when:
  • PIH levels decrease with a fall in estrogen
  • Prior to menstruation
  • Toward the end of pregnancy
  • Stimulated with infant nursing

Adrenal (Suprarenal) Gland

• The adrenal gland sits on the kidney.
• It's enclosed by a fibrous capsule and a fat pad.
• Structurally and functionally, it is composed of two glands:
  • Adrenal Cortex
  • Adrenal Medulla

Adrenal Gland: Adrenal Cortex

• Produces corticosteroids.
• Composed of three zone layers: - Zona glomerulosa. Produces mineralocorticoids, like aldosterone. - Zona fasciculata. Produces Glucocorticoids and androgens, like Cortisol and sex hormones. - Zona reticularis. Produces Glucocorticoids and Gonadocorticoids, like Cortisol and sex hormones.

Mineralocorticoid: Aldosterone

• Target Tissue - kidneys
• Reduces sodium secretion in the kidney.
  • Causes water retention
• Enhances sodium reabsorption: - Urine - Sweat - Gut
• Raises blood pressure.
• Regulation - To be covered in chapter 23

Glucocorticoids: Cortisol

• Target tissue: Most body cells.
• Effects:
  • Regulate metabolism.
  • Adapt to stress and repair tissues. (Anti-inflammatory effect) _ Gluconeogenesis — promotes glucose formation from fat and protein.
  • Enhances epinephrine's vasoconstrictive effects.

Cortisol Regulation

• CRH (corticotropin releasing hormone) is produced by the hypothalamus.
• ACTH (adrenocorticotropic hormone) is released from the pituitary in response to CRH.
• ACTH stimulates adrenal gland to produce cortisol.
• Elevated cortisol inhibits release of CRH and ACTH. The hypothalamus responds to level of cortisol.

Cortisol Abnormalities

• Elevated cortisol levels: Cushing's Syndrome
• Depressed cortisol levels: Addison's

Gonadocorticoids Effect and Regulation

• Effect
  • Contribute to the onset of puberty.
  • Reponsible for sex drive.
  • Changes in metabolism.
• Regulation
  • By FSH and LH.

Adrenal Gland: Adrenal Medulla

• Part of the autonomic nervous system.
• Hormones
  • Catecholamines
    • Epinephrine
    • Norepinephrine
    • Dopamine (trace amounts)
• Acts as both neurotransmitters and hormones.

Sympathetic Division of ANS (Autonomic Nervous System)

• Preganglionic neurons.
• Postganglionic neurons.
• Regions of spinal cord: - Cervical. - Thoracic. - Lumber. - Sacral.

Adrenal Medulla: Catecholamines

• Origin is from chromaffin cells (modified postganglionic neurons) and target tissue.
• Target tissue: nearly all tissue.

Catecholamines Effects and Regulation

• Effects
  • Fight - or - flight response.
    • Elevates heart rate.
    • Pupils dilate.
    • Elevates blood pressure.
    • Blood shunted to brain.
• Sympathetic control.

Endocrine System : Thyroid Gland

• Largest of the pure endocrine glands.
• Anterior neck location.
• Structure: Butterfly shaped.
  • Two Lobes
  • Isthmus

Thyroid Gland . Micro Structure

• Composed of hollow spherical follicles.
• Follicular cells: cuboidal or squamous epithelial cells that form the walls.
  • Produce thyroid hormone:
    • Thyroxine (T4).
    • Triiodothytonine (T3).
• Parafollicular cells (C cells)

Thyroid Gland : Thyroid Hormones

• Originates from follicular cells.
• Target cells: all cells besides:
  • Spleen
  • Testis
  • Uterus
  • Thyroid Gland
  • Adult brain

Thyroid Hormones Effect

• Calorigenic Effect: (increase metabolism) Increases:
  • Alertness/reflexes
  • Respiratory rate
  • Heart rate
    • Strength of Heartbeat = BP
  • Appetite
  • Breakdown of carbs, fats, proteins
  • GH (growth hormone)
  • Fetal development

Thyroid Hormones Regulation

• TRH - thyrotropin-releasing hormone
• TSH - thyroid stimulating hormone

Regulation :: Thyrotropin Release Hormone

• Overcomes the negative feedback loop.
• In conditions requiring increased body.
  • Energy need such as pregnancy and prolonged cold.

Regulation:: Thyroid Stimulating Hormone

• TSH rises in response to declining T4 levels.
• TSH is suppressed by
  • Rising T4 levels
  • Somatostatin
  • Rising levels of glucocorticoids
  • Sex hormones

Thyroid Hormones Abnormalities

• Enlarged thyroid gland - goiter.

Thyroid Hormones Abnormalities

• Decreased: hypothyroidism
• Congenital iodine deficiency syndrome
• Increased - hyperthyroidism
• Graves' disease

Thyroid Gland : Calcitonin

• Origin - parafollicular cells OR C cells -Targets bone tissue, more important during. Childhood

Calcitonin Effect

• Responds to high blood calcium.
• INHIBITS OSTEOCLAST ACTIVITY - Decrease bone reabsorption -Decrease Calcium release.
• Stimulates uptake of calcium into the bone matrix ( by activity of which cell?)

Calcitonin - Regulation

• Releases Stimulated by Levels of blood Calcium.
• Releases Inhibited By Dropping Calcium levels

Endocrine System : Parathyroid Gland

• Tiny glands imbedded in the thyroid.
• Usually 4, may be up to 8!
• Produces parathyroid Hormone (PTH)

Parathyroid gland :Parathyroid Hormones

• Origin: chief cells. -Targets skeletal, kidney and intestine.

Parathyroid Hormones : Effects

• Stimulates osteoclasts to release - calcium and phosphates into the blood,
• Inhibits osteoblasts.
• Enhances reabsorption of calcium in the kidneys.
• Increase absorption of calcium in the intestine (by activity of calcitriol - vit. D)
  • Vitamin D

Parthyroid Hormone :Abnormalities

• Increased - hyperparathyroidism

Endocrine System :Pancreas

• Located behind the stomach.
• Mixed gland - endocrine AND exocrine.
• Made of up acinar cells and pancreatic islets.
  • (IsLET cells of : Langerhans)

Pancreas :Hormones

• Insulin: Anabolic (converts smaller molecules into larger ones)
  • Glucose → Glycogen
  • Amino Acids to → Proteins.
• Glucagon
  • Catabolic ( breaking down larger molecules into their subunits!)
  • Reverse everything above

Pancrease: Insulin

• Origin & Target Tissues
  • Orgin is beta cells of the pancreatic islets
  • Target Tissue : muscle & fact cells.
• Insulin effect:
  • Insulin used to absorb glucose
• Excludes:
  • Liver (glycogenesis) ,Kidney and Brain
• All 3 absorb and use glucose without insulin

Insulin : Effects

• Lower blood glucose levels
• Enhances membrane transport of glucose into body cells
• Inhibits breakdown of glycogen to glucose. this is the action of glucagon!
• Inhibits conversion of amino acids and fats to glucose

Insulin :Regulation

• Stimulated by:

  • Elevated blood sugar levels
  • Rising levels of amino acids and fatty acids
  • Acetylcholine released by. Parasymphatetic nerves

• Inhibited By

  • Dropping serum glucose
  • Somatostatin (GHIH)

Insulin :Abnormalities

• Diabetes Mellitus (DM):
• Type 1
  • (IDDM) -Aunto-Imme disease
• Type 2
  • (NIDDM) - Reduced sensitivity to insulin
• Too much
  • Hypoglycemia

Pancreas: Glucagon

• Origin Alpha Cells of the pancreas islets.
• Target Tissue- Liver!
  • ( Islet of langerhaus)

Glucagon :Effects

• Raises blood glucose levels
• Breakdown of glycogen to glucose ( -Glucose-Glycogenolysis) - Synthesis of Glucagon (glucoseoenogensis) - Release of glucose from the liver.

Glucagon :Regulation

• Released when levels of blood glucose levels drop
• Stimulated by:
  • Symphatetic Activity
  • Rising amino acids
• Insulin antagonizes
  • all effects
• Inhibited when: -Rising blood sugar
  • Somatostatin (GHIh)

Endocrine System: Pineal Gland

• Tiny pine corn shape -Located in epitha. -Secretion of: Melatonin

Pineal :Melatonin

• Origin and Target Tissues
  • Origin: Pinealocytes
  • Target Tissue: Suprachiasmatic Nuclei.

Melatonin :Effect & Regulation

• Responsible for:Regulation of sleep cycles
  • Causes drowsiness
  • Circadian Rhythm Regulation :
  • Light responsive
  • Peak levels at night
  • Lowest levels @Noon

Explore hormone functions, regulatory mechanisms, and key endocrine organs. Understand hormone release, feedback loops, and differences between the endocrine and nervous systems. Learn about hormones that may be affected by certain drugs.