Endocrine System Quiz

Endocrine Physiology Overview

• Endocrinology is the study of hormones and endocrine organs.
• The endocrine system acts with the nervous system to coordinate and integrate body cell activities
• Endocrine system responses are slower but longer lasting than nervous system responses.
• Endocrine system influences metabolic activities
• The endocrine system controls and integrates reproduction, growth, development and maintenance of electrolyte, water, and nutrient balance of blood; regulation of cellular metabolism and energy balance; and mobilization of body defenses.

Chemical Messengers

• Hormones are long-distance chemical signals that travel in blood or lymph.
• Autocrines are chemicals that exert effects on the same cells that secrete them.
• Paracrines are locally acting chemicals that affect cells other than the ones that secrete them.
• Autocrines and paracrines are considered local chemical messengers and aren't part of the endocrine system.

Mechanisms of Hormone Action

• Hormones circulate systemically, but only cells with receptors for a specific hormone are affected.
• Hormones alter target cell activity in several ways.
• Some hormones alter plasma membrane permeability and/or membrane potential.
• Other hormones stimulate the synthesis of enzymes or other proteins; activate or deactivate enzymes; or induce secretory activity.
• Some hormones stimulate mitosis.

Mechanisms of Hormone Action - Receptor Location

• Water-soluble hormones (all amino-acid-based hormones, except thyroid hormone) act on plasma membrane receptors and use G protein second messengers.
• Water-soluble hormones include Cyclic AMP, PIP2-Calcium
• Lipid-soluble hormones (steroid and thyroid hormones) act on intracellular receptors, directly activating genes to enter cells.

Plasma Membrane Receptors and Second-Messenger Systems

• Hormone (first messenger) binds to the receptor.
• Receptor activates a G protein.
• G protein activates or inhibits an effector enzyme.
• Effector enzyme generates a second messenger.
• Second messenger activates protein kinases.
• Protein kinases phosphorylate proteins.
• Phosphorylated proteins cause the cell's response and amplification cascade.
• Some second messenger systems use cyclic AMP (cAMP), or PIP2-calcium signal for different cell responses

PIP2-calcium signaling mechanism

• Hormone-activated G proteins activate phospholipase C.
• Activated enzyme cleaves phospholipids, forming diacylglycerol (DAG) and inositol trisphosphate (IP3).
• DAG activates protein kinases.
• IP3 causes Ca2+ release from intracellular storage sites.
• Calcium acts as a messenger, altering enzyme activity.

Intracellular Receptors

• Steroid hormones and thyroid hormones diffuse into target cells.
• They bind to intracellular receptors within the target cells.
• The receptor-hormone complex travels to the nucleus.
• The hormone-receptor complex binds to specific DNA regions, promoting/inhibiting DNA transcription.
• This process results in new proteins or changes affecting metabolic actions.

Target Cell Activation

• Target cell specificity depends on the blood level of hormone.
• Relative number of receptors or in the target cell.
• The affinity of receptor binding between receptor and hormone.
• Hormones influence receptor numbers.
• Up-regulation occurs in low hormone levels which increase receptor numbers.
• Down-regulation occurs in high hormone levels which reduces receptor numbers,

Control of Hormone Release

• Endocrine gland stimuli include hormonal, neural, and humoral stimuli.

Hormones in the Blood

• Hormones circulate freely or bound to plasma proteins.
• Steroid and thyroid hormones travel bound.
• Others circulate freely.
• Hormone concentration reflects the rates of hormone release.
• Hormone half-life is the time needed for the hormone's blood level to reduce by half.

Interaction of Hormones at Target Cells

• Multiple hormones may act on the same target cell.
• Permissiveness is when one hormone is needed for the action of another hormone.
• Synergism is when the actions of multiple hormones enhance each other.
• Antagonism occurs when multiple hormones oppose each other's actions.

Comparison of Lipid- and Water-Soluble Hormones

• Lipid-soluble hormones are usually steroids or thyroid hormones.
• Lipid-soluble hormones have longer half-lives in blood.
• Lipid-soluble hormones act on intracellular receptors.
• Water-soluble hormones are most amino acid based hormones.
• Water-soluble hormones have shorter half-lives in blood.
• Water-soluble hormones act on membrane receptors.

Hypothalamus & Pituitary

• The hypothalamus and pituitary glands are essential for regulating many body functions.
• The hypothalamus controls pituitary hormone release through neural or hormonal pathways.
• The anterior pituitary is controlled by hormonal pathways of releasing and inhibiting hormones from the hypothalamus.
• The posterior pituitary releases hormones synthesized in the hypothalamus via neural pathways.

Posterior Pituitary and Hypothalamic Hormones

• Oxytocin is associated with uterine contractions and milk ejection.
• ADH (vasopressin) regulates water balance.
• ADH deficiency/excess can cause many health problems.

Anterior Pituitary Hormones

• The main anterior pituitary hormones include growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL).
• Most are proteins.
• TSH and ACTH, FSH and LH are tropic hormones.

Growth Hormone (GH)

• GH has metabolic and growth effects on the body
• Direct actions affect metabolism, including increase blood fatty acids, decrease glucose uptake, and glycogen breakdown to release glucose into the blood.
• Indirect actions involve growth via growth hormone like factors promoting growth of cartilage, bone and skeletal muscle.
• Imbalances include gigantism in children and acromegaly in adults.

Thyroid-stimulating Hormone (Thyrotropin)

• Produced by thyrotropic cells of the anterior pituitary.
• Stimulates normal development and secretory activity of the thyroid.

Adrenocorticotropic Hormone (ACTH)

• Produced by corticotropic cells of the anterior pituitary.
• Stimulates adrenal cortex to release corticosteroids.
• Daily rhythm triggered by hypothalamic CRH.

Gonadotropins

• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) stimulate gamete production.
• FSH stimulates gamete products.
• LH promotes production of gonadal hormones.
• Regulation of release triggered by gonadotropin-releasing hormone (GnRH).
• Release is suppressed by gonadal hormones.

Prolactin (PRL)

• PRL is produced by prolactin cells of the anterior pituitary.
• Stimulates milk production.
• Role in males not well understood.
• Release regulated by prolactin-inhibiting hormone and suckling reflexes.
• Hypersecretion leads to inappropriate lactation.

Thyroid Gland

• The thyroid gland produces thyroid hormones (T4 and T3).
• T4 and T3 have major metabolic and developmental effects regulating virtually every cell in the body.
• They increase metabolic rate and heat production, influencing skeletal growth, nervous system development, reproduction, and blood pressure.
• Control of release is through negative feedback regulation.
• Homeostatic imbalances can cause myxedema in adults and cretinism in infants.

Calcitonin

• Calcitonin is produced by parafollicular cells.
• It is the antagonist of parathyroid hormone.
• It has lower than normal doses.
• It regulates calcium levels.

Parathyroid Glands

• Parathyroid glands regulate calcium levels via actions through the body.
• PTH is the main hormone produced in the parathyroid.
• PTH increases calcium levels through the bone, kidneys and intestines.
• Imbalances in PTH can cause bones to soften, deform, kidney stones or tetany

Adrenal Glands

• Adrenal glands consist of cortex and medulla regions.
• Corticosteroid hormones (mineralocorticoids, glucocorticoids, and gonadocorticoids) are secreted in the cortex.
• The adrenal medulla releases epinephrine and norepinephrine, leading to short-term stress response.
• Imbalances can lead to several health issues.

Mineralocorticoids

• Mineralocorticoids like Aldosterone regulate electrolytes like sodium and potassium, vitally important for fluid balance, blood volume and pressure.
• Aldosterone increases sodium reabsorption and water retention in the kidneys.
• It also promotes the excretion of potassium.
• Its release is triggered by decreasing blood volume, blood pressure, and rising potassium levels.
• Imbalances may result in serious health problems.

Glucocorticoids

• Glucocorticoids like Cortisol are important in regulating blood glucose and pressure.
• They help maintain constant blood glucose levels in the body during stress, while promoting glucose production and utilization.
• Cortisol enhances metabolism in many tissues and affects immune function.
• Homeostatic imbalances can lead to Cushing's syndrome or Addison's disease.

Gonadocorticoids

• Gonadocorticoids are weak androgens (male hormones).
• They convert to androgens and estrogens.
• They play a role in the onset of puberty, appearance of secondary sex characteristics, sex drive in women (estrogen in postmenopausal women).

Adrenal Medulla

• Adrenal medulla releases epinephrine, norepinephrine and are part of the body's stress response affecting metabolic activity, dilation of the bronchi, heart and skeletal muscle blood flow.
• Imbalance results in several physiological conditions.

Pancreas

• Pancreas produces hormones regulating blood glucose levels.
• Glucagon increases blood sugar levels.
• Insulin lowers blood sugar levels, increasing glucose uptake.
• Imbalances in these hormones lead to many conditions including hypo and hyperglycemia.
• Imbalances may lead to diabetes.

Factors Influencing Insulin Release

• Blood glucose, amino acids and fatty acids are primary factors that trigger insulin release.
• Parasympathetic neurons and hormones like glucagon lead to insulin release.

Homeostatic Imbalances of Insulin

• Diabetes mellitus is a common result from insulin imbalances and has several types.

Diabetes Mellitus: Signs

• Polyuria, polydipsia and polyphagia collectively form the three cardinal signs of diabetes mellitus (DM) indicating issues with blood glucose regulation.

Gonads

• Gonads are reproductive organs producing steroid sex hormones that influence reproductive organs.

Ovaries and Placenta

• Ovaries produce estrogen and progesterone.
• These hormones are essential for reproductive development.
• The placenta also produces estrogen, progesterone and human chorionic gonadtropin (hCG) to support pregnancy.

Testes

• Testes produce testosterone, which is essential for male reproductive function.
• It triggers male reproductive organ maturation and secondary sexual characteristics.