Endocrine Study guide

KINE 191: Lecture 3 - Endocrine System

Learning Objectives

• Understand the types of intercellular communication, their importance, mechanisms, and effects.

• Identify the major organs and tissues of the endocrine system and their locations in the body.

Overview of Hormones

• Definition of Hormone: A hormone is a mediator molecule used by the endocrine system, released in one part of the body to regulate activity in other parts.

  • Most hormones are released by endocrine glands, entering interstitial fluid then bloodstream to reach target cells through specific receptors.

• Glands Involved: The endocrine system encompasses various glands including the pituitary, thyroid, parathyroid, adrenal, pineal glands, and gonads.

Differences Between Nervous and Endocrine Systems

Functions

• Both systems maintain homeostasis; they can function independently or collaboratively.

Mediators

• Nervous System: Uses nerve impulses with neurotransmitters at synapses.

• Endocrine System: Uses hormones to regulate body activities.

Site of Mediator Action

• Nervous System: Effects are local at the site of release.

• Endocrine System: Hormones can act at distant sites.

Time to Onset of Action

• Nervous System: Milliseconds.

• Endocrine System: Seconds to minutes to days.

Duration of Action

• Nervous System: Generally brief.

• Endocrine System: Effects can last longer (seconds to days).

Specificity of Action

• Nervous System: Effects are specific (e.g., contraction of specific muscles).

• Endocrine System: Hormones may affect multiple physiological processes (e.g., oxytocin affects labor and bonding).

Consequences of Communication

• Nervous System: Facilitates quick actions and responses.

• Endocrine System: More involved in sustaining the internal body's environment, responding slower to stimuli.

Types of Glands

1. Endocrine Glands

• Secrete hormones into interstitial fluid surrounding the secretory cells, then the hormones diffuse into capillaries and they are then carried to target cells throughout the body via bloodstream.

2. Exocrine Glands

• Secrete their products into ducts that carry their secretions either into the lumen of an organ or outer surface (e.g., sweat glands, salivary glands).

• Examples: sweat, sebaceous, mucous, and digestive glands.

3. Hormone-Secreting Organs

• Some non-endocrine organs (e.g., thymus, pancreas, ovaries, etc.) also secrete hormones as secondary functions.

Hormone Influences

• Hormones influence only target cells with specific receptors for that hormone; upon binding to a receptor, they initiate a cellular response.

• Many drugs prevent certain hormones from binding to its target receptor, therefore prevents the hormone from having its specific action.

  • Ex. Beta Blockers block the effect of norepinephrine and epinephrine on heart, which slows the heart rate and lower blood pressure.

Chemical Classes of Hormones

Lipid-Soluble Hormones

• Carried in the bloodstream bound to a transport proteins; they diffuse into target cells and bind to receptors within their target cells, altering gene expression which causes new protein to be made.

• The new proteins cause the responses typical of that hormone

  • Examples: Steroids (e.g., aldosterone, testosterone), Thyroid Hormones (T3 and T4), Nitric Oxide.

Water-Soluble Hormones

• Do not require transport proteins to carry them into bloodstream. Since they are not lipid soluble, they cannot diffuse through lipid bilayer of the plasma membrane, thus they bind to receptors on the plasma membrane of target cells.

• A water-soluble hormone (the first messenger), diffuses from the blood through interstitial fluid and then binds to its receptor at the surface of the cell's plasma membrane

  • Examples: Amine hormones (e.g., epinephrine, norepinephrine), peptide hormones (e.g., ADH, Ocytocin, insulin). Protein hormones (e.g., GH, FSH)

Control of Hormone Secretion

• Hormone release occurs in bursts and is regulated by:

  1. Signals from the nervous system

  2. Chemical changes in the blood

  3. Presence of other hormones

Examples of Regulation

• Nervous System Stimulation: Triggers endocrine glands to release its hormones.

• Chemical Changes: Presence of certain chemicals modulates the hormonal release by endocrine gland. Blood calcium levels regulates the secretion of PTH & calcitonin hormones.

• Hormonal Effects: A hormone may synergistically or antagonistically affect the release of another hormone. TSH stimulates the release of T3 and T4 from the thyroid gland. Presence of PTH stimulates the kidneys to release Calcitriol

Feedback Mechanisms

• Negative Feedback: Elevations in hormone levels inhibit further production (e.g., elevated T3 and T4 inhibit TRH and TSH).

• Positive Feedback: Some processes, like childbirth, enhance hormone releases (e.g., oxytocin during labor).

Pituitary Gland and Hypothalamus

• The hypothalamus-pituitary complex is the command center of the endocrine system, managing both direct action on target tissues, as well as hormones that regulate the synthesis and secretion of other glands.

  • In addition, the hypothalamus–pituitary complex receives stimuli by the nervous system that must be translated into hormones that can initiate a response.

  • The hypothalamus is a structure of the diencephalon of the brain located anterior and inferior to the thalamus.

    •It has both neural and endocrine functions, producing and secreting hormones.

• Anterior Pituitary: Secretes hormones regulated by hypothalamic releasing and inhibiting hormones via the hypophyseal portal system.

  • Produces six key hormones:

  • Human Growth Hormone (HGH): promotes growth of body cells, protein synthesis and tissue repair),

  • Thyroid Stimulating Hormone (TSH): Stimulates secretion of T3 & T4 by the thyroid gland, regulates metabolism , energy balance.

  • Adrenocorticotropin (ACTH): stimulates the adrenal cortex to release a stress hormone cortisol

  • Follicle-stimulating hormone(FSH): promotes sperm production in men , stimulates ovaries to produce estrogen and develops eggs in females

  • Luteinizing hormone(LH): stimulates testosterone production in men , stimulates ovulation in women

  • Prolactin (PRL) produces breast milk by mammary glands

  • Melanocyte-stimulating hormone MSH) can cause darkening of the skin

• Posterior Pituitary: Does not produces hormones but it Stores and secretes ADH and oxytocin produced by the hypothalamus.

  • Antidiuretic hormone (ADH): increases water reabsorption in the kidney which reduces urine volume

  • Oxytocin stimulates milk flow during labor, promotes labor during birth, promotes bonding b/w mother and child

Disorders of the Anterior Pituitary

1. Giantism: Excess hGH in childhood, causing abnormally tall growth.

2. Acromegaly: Excess hGH in adulthood leads to thickened bones in hands, feet, and jaw.

Thyroid Gland

• Butterfly-shaped gland located anterior to the trachea and inferior to the larynx; requires iodine.

• Produces T3& T4 hormones in response to bidning of TSH from the Anterior pituitary. which produces an increase in the body’s basal metabolic rate which elevates body temp

• Produces calcitonin, which lowers blood calcium levels during high calcium concentrations.

• Disorders include goiter, an enlargement of the thyroid gland due to iodine deficiency. usually accompanied by by hypothyroidism

Parathyroid Glands

• Small glands located on the posterior surface of the thyroid, producing PTH which regulates calcium levels by stimulating bone resorption and increasing intestinal absorption.

• Regulated via a negative feedback mechanism based on calcium levels.

2 Adrenal Glands

• Located on top of the kidneys, one of the function is responding to stress- physical, psychological or both. Have an exterior cortex, and an inner medulla

  • Adrenal Cortex has 3 Zones: each secretes it own set of hormones

    1. Zona Glomerulosa (outermost layer): Produces aldosterone, important in regulating mineral balance (Na+, K+ in urine, sweat, and saliva)

       1. It is released in response to elevated blood K+, or low blood pressure, or low blood volume. In response, aldosterone increases the excretion of K+ and the retention of Na+, which in turn increases blood volume and blood pressure.

    2. Zona Fasciculata (Middle region): Produces cortisol, influencing glucose metabolism during stress.

    3. Zona Reticularis (deepest layer): Produces sex hormones called androgens (DHEA).

       1. During puberty and most of adulthood, androgens are produced in the gonads (male testes and female ovaries). The androgens produced in the zona reticularis supplement the gonadal androgens

          

  • Adrenal Medulla: Releases epinephrine and norepinephrine for short-term stress which is mediated by the sympathetic nervous system .

Pineal, Gonads, and Pancreas

Pineal Gland

• Is part of the diencephalon, inferior but somewhat posterior to the thalamus. Involved in sleep regulation by releasing melatonin.

Testes and Ovaries

• Testes are oval, paired, glands that lie in the scrotum. They produce testosterone which Regulates sperm production, stimulates and maintains male secondary sex characteristics (those that appear during puberty).

  • In Boys:

    •Testicles enlarge

    •Pubic hair appears

    •Body grows taller and heavier

    •Penis enlargens

    •Voice deepens

• Ovaries , are paired oval bodies found within the female pelvic cavity. They produce:

  • Estrogen and progesterone: Together with FSH and LH regulate the female menstrual cycle and maintain pregnancy

  • Relaxin : increases flexibility of the pubic symphysis during pregnancy

  • Inhibin : inhibits secretion of FSH from the anterior pituitary

Pancreas

• Serves both exocrine (digestive enzymes) and endocrine (glucagon and insulin) functions, regulating blood glucose levels.

Disorders of the Pancreas

• Diabetes Mellitus: A major endocrine disorder splitting into Type 1 (autoimmunity against beta cells) and Type 2 (insulin resistance), leading to severe health complications.