Cell Communication Quiz

Endocrine System Overview

• The human body has 100 trillion cells, organized into four basic tissues, which then form organs.
• Cell communication is vital for preserving organ functions and maintaining homeostasis.
• There are six major forms of intercellular communication.

Types of Cell Communication

• Direct communication: Mediated by gap junctions, allowing small signaling chemicals to pass between cells.
• Autocrine communication: Local hormones (paracrine factors or cytokines) are secreted from a cell and act on the same cell.
• Paracrine communication: Local hormones (paracrine factors or cytokines) are secreted into extracellular fluids to affect nearby target cells.
• Juxtacrine communication: Local hormones are held on the plasma membrane, and the target cell binds to or links up with the bound factor, involved in growth and differentiation.
• Synaptic communication: Neurotransmitters are released from a presynaptic cell (usually a neuron) to travel across a gap and bind to a postsynaptic target cell (e.g., a second neuron or muscle cell).
• Endocrine communication: Hormones are secreted into extracellular fluids, enter the bloodstream, and travel to affect distant target cells.

Mechanisms of Intercellular Communication

• Direct communication relies on gap junctions, passing ions and small solutes.
• Paracrine communication acts locally through extracellular fluid.
• Endocrine communication uses the circulatory system to target distant cells.
• Synaptic communication uses neurotransmitters across synaptic clefts.

Cell Communication Overview

• For successful communication, target cells must have protein receptors for messengers released from other cells.
• Messenger binding to a receptor activates the receptor, triggering intracellular events (signal transduction).

Endocrine System Components

• Endocrine glands/tissues: Produce hormones.
• Hormones: Chemical messengers secreted into the bloodstream to stimulate responses in other tissues or organs.
• Target cells: Possess receptors specific to the hormone.

Endocrine vs Exocrine Glands

• Exocrine glands: Have ducts that carry secretions to a surface or organ cavity. Products have extracellular effects (e.g., food digestion).
• Endocrine glands/tissues: Lack ducts, releasing hormones into tissue fluids, then distributing them through highly permeable capillary networks. Products have intracellular effects, altering target cell metabolism.

Communication Systems: Nervous vs Endocrine System

• Nature of communication: Nervous system - electrical and chemical; Endocrine system - chemical only
• Speed and persistence: Nervous system - fast, brief response; Endocrine system - slow, prolonged response
• Adaptation to long-term stimuli: Nervous system - quickly adapts; Endocrine system - response persists
• Area of effect: Nervous system - targeted, specific areas; Endocrine system - general, widespread effects

Nervous and Endocrine Systems Interaction

• Some chemicals function as both hormones and neurotransmitters (e.g., norepinephrine, cholecystokinin).
• Neuroendocrine cells secrete hormones (e.g., oxytocin, catecholamines).
• Both systems coordinate their effects to modulate target cell activity.

Endocrine System Functions

• Reproduction, growth, development, activation of body defenses, salt and water balance, nutrient balance, and cellular metabolism.

Major Endocrine Organs

• Hypothalamus, pituitary (adenohypophysis and neurohypophysis), pineal gland, thyroid gland, parathyroid glands, thymus, adrenal glands (cortex and medulla), pancreas, ovaries, testes.

Hormone Names and Abbreviations

• A table listing various hormones, abbreviations, and their sources.

Hypothalamus Location and Role

• Shaped like a flattened funnel, forming the floor and walls of the third ventricle.
• Controls the anterior pituitary through releasing and inhibiting hormones.
• Produces oxytocin and ADH, which are released by the posterior pituitary.
• Controls the release of epinephrine and norepinephrine from the adrenal medulla.

Pituitary Gland (Hypophysis)

• Suspended from the hypothalamus by a stalk (infundibulum).
• Housed in the sella turcica of the sphenoid bone, approximately 1.3 cm in diameter.
• Two major parts: adenohypophysis (anterior pituitary) and neurohypophysis (posterior pituitary). The adenohypophysis arises from the hypophyseal pouch (outgrowth of pharynx), the neurohypophysis is a down-growth of the hypothalamus (neural tissue).

Embryonic Development

• Diagram illustrating the embryonic development of the pituitary and thyroid glands.

Adenohypophysis

• Also known as the anterior pituitary. Details of location related to hypothalamus.

Hypothalamic-Hypophyseal Portal System

• Hormones from the hypothalamus travel through a portal system to the anterior pituitary.
• Anterior pituitary hormones then enter a second capillary bed to join the general circulation.

Anterior Pituitary Hormones

• Principle hormones and target organs are shown.

Pituitary Hormones-Anterior Lobe

• Trophic hormones target other endocrine glands, including gonadotropins, TSH, ACTH, PRL, and GH.

Hormone Actions: Anterior Lobe

• Actions of FSH, LH, TSH, and ACTH.
• PRL (prolactin) and GH (growth hormone) actions, including growth effects and metabolic regulation.

Growth Hormone

• Secreted by somatotropes and promotes tissue growth.
• Stimulates protein synthesis, and promotes the use of fats in energy metabolism, while sparing glucose.
• Crucial for growth in childhood and adolescence.

Growth Hormone and Aging

• GH levels fluctuate throughout the day, and are higher during sleep and after exercise, lower after carbohydrate intake.

Neurohypophysis

• Also called the posterior pituitary. Details of hypothalamic nuclei related to posterior pituitary.

Pituitary Hormones - Posterior Lobe

• The posterior pituitary stores and releases oxytocin and ADH.

Hormone Actions: Posterior Lobe

• Effects of ADH (e.g., water retention in kidneys).
• Effects of oxytocin (e.g., labor contractions, milk ejection).

Control of Pituitary

• Pituitary hormones are not secreted at a constant rate, with examples of GH and hormonal variations during the menstrual cycle.
• The timing of hormone release is regulated by hypothalamic hormones and other brain centers.

Control of Anterior Lobe of Pituitary

• Releasing hormones produced by the hypothalamus control the secretion of other hormones.

Control of Posterior Lobe of Pituitary

• Neuroendocrine reflexes, in response to neural signals (e.g., oxytocin release in infants/babies).

Pineal Gland Location

• Located in the brain; anatomical details.

Pineal Gland

• Peaks in secretion between ages 1 and 5; by puberty it declines to approximately 75% lower.
• Produces serotonin by day, and converts it to melatonin at night.
• May regulate timing of puberty, and removal can cause premature sexual development.
• Melatonin levels are affected by phototherapy.

Thymus

• Located in the mediastinum, superior to the heart, and involutes after puberty.

Thyroid Gland Anatomy

• Largest endocrine gland; high rate of blood flow, situated anterior/lateral to the trachea.
• Composed of two lobes connected by the isthmus.

Histology of the Thyroid Gland

• Structure of thyroid follicles, follicular cells, and colloid.

Thyroid Gland

• Thyroid follicles contain colloid (thyroglobulin).
• Follicular cells secrete T3 and T4 (thyroid hormones).
• Thyroid hormones increase metabolic rate, body’s O₂ consumption and heat production, respiratory rate, and heart rate. Stimulates digestive system, growth of bone, skin, hair, nails, and nervous system activities.

Parathyroid Glands Location and Role

• Located on the posterior surface of the thyroid gland.
• Parathyroid hormone (PTH) regulates blood Ca²⁺ levels.

Adrenal Gland

• Comprises the adrenal cortex (epithelial origin) and adrenal medulla (neural origin).
• Adrenal cortex possesses three layers: Zona glomerulosa, Zona fasciculata and Zona reticularis.

Adrenal Medulla

• The medulla acts as a sympathetic ganglion.
• Contains chromaffin cells. Stimulates the release of catecholamines (epinephrine, norepinephrine), and dopamine.

Adrenal Cortex

• Layers comprised of zona glomerulosa, zona fasciculata and zona reticularis.

Adrenal Cortex cont.

• Mineralocorticoids (zona glomerulosa) - control electrolyte balance.
• Glucocorticoids (zona fasciculata) - regulate metabolism, including fat and protein catabolism, gluconeogenesis, and glucose release in relation to stress.
• Sex steroids (zona reticularis) - important in the production of androgens and estrogen.

Adrenal Cortex Hormones

• Corticosteroids including aldosterone, cortisol androgens.

Pancreas

• Retroperitoneal, inferior and dorsal to the stomach.
• Contains 1-2 million islets that produce hormones, and 98% of the organ produces digestive enzymes.

Pancreatic Hormones

• Insulin (secreted by beta cells) - lowers blood glucose levels.
• Glucagon (secreted by alpha cells) - raises blood glucose levels.
• Somatostatin (secreted by delta cells) - inhibits the release of other pancreatic hormones

Glucose Regulation

• Hyperglycemic hormones raise blood glucose (GH, epinephrine, norepinephrine, glucagon, glucocorticoids).
• Hypoglycemic hormones lower blood glucose (insulin).

Ovary

• Granulosa cells produce estradiol in the first half of the menstrual cycle.
• Corpus luteum (from follicle cells) produces progesterone and estradiol.
• These hormones influence the development and regulation of the female reproductive system, including menstrual cycle and support pregnancy.

Testes

• Interstitial cells of Leydig produce testosterone and some estrogen.
• Important for male reproductive system, sperm production, and sex drive.

Endocrine Functions of Other Organs

• Heart (atrial natriuretic peptide): Released when blood pressure increases, influencing blood volume and blood pressure.
• Skin (vitamin D3): Important for calcium regulation.
• Liver (erythropoietin): Stimulates bone marrow and contributes to red blood cell production; produces angiotensinogen, source of IGFs, and converts vitamin D3 to calcidiol.

Endocrine Functions of Other Organs cont.

• Kidneys: Produce erythropoietin, stimulate bone marrow, converts vitamin D3 to calcitriol, and regulate calcium absorption and excretion.

• Stomach and small intestines: Produce enteric hormones that coordinate digestion.

• Placenta: produces hormones essential for maintaining pregnancy, fetal development, and mammary gland function.

Chemical Classes of Hormones

• Lipid derivatives (steroidal hormones, eicosanoids)
• Amino acid derivatives (monoamines, thyroid hormones)
• Peptide hormones (glycoproteins, short polypeptides, small proteins)

Hormones Derived from Lipids

• Eicosanoids (prostaglandins, leukotrienes).
• Steroid hormones (estrogen, progesterone, testosterone, cortisol, aldosterone).

Hormone Synthesis: Steroid Hormones

• Steroid hormones are derived from cholesterol and have a characteristic four-ringed structure.

Amino Acid Derivatives

• Monoamines and catecholamines (epinephrine, norepinephrine, dopamine).
• Melatonin production.
• Thyroid hormones (T3 and T4).

Hormones Derived from Peptides

• Glycoproteins (thyroid stimulating hormone, follicle stimulating hormone, luteinizing hormone
• Short polypeptides and small proteins (ADH, oxytocin, ACTH, calcitonin, growth hormone, prolactin, parathyroid hormone, insulin, glucagon, somatostatin).

Control of Hormone Release

• Humoral stimuli (e.g., blood glucose levels).
• Neural stimuli (e.g., nervous signals for oxytocin release).
• Hormonal stimuli (e.g., positive and negative feedback loops).

Humoral Stimuli: Control of Parathyroid Hormone Levels

• Details about how dropping blood calcium levels trigger parathyroid hormone secretion

Neural Stimuli: Feedback Loop with Oxytocin

• Detail about neural reflexes involving oxytocin release in response to signals from nerve endings and higher brain centers.

Hormonal Stimuli: Negative Feedback Loop Control of Thyroid Hormone Levels

• Negative feedback loop mechanism in control of thyroid hormones.

Hormone Transport

• Hydrophobic hormones (steroid and thyroid hormones) require carrier proteins for transport in blood .
• Hydrophilic hormones (monoamines and peptides) mix easily with blood.

Hormone Receptors

• Located on plasma membranes, mitochondria, other organelles, or in the nucleus.
• Receptor specificity and saturation.

Hormone Mode of Action

• Hydrophobic hormones directly activate genes; hydrophilic hormones often employ second messenger systems.

Intracellular Hormone Receptors

• How hydrophobic hormones penetrate the plasma membrane, find receptors in the nucleus, and activate gene expression.

Thyroid Hormone Effects

• Details about thyroid hormone's effects on target cells.

Extracellular Hormone Receptors

• How hydrophilic hormones use second messengers like cAMP to act on target cells.

Termination of Signal

• How hormone signals are deactivated.

Hydrophilic Hormones: Mode of Action Other 2nd Messengers

• Different second messengers employed (e.g., Diacylglycerol (DAG) and inositol triphosphate (IP3)).

Modes of Hormone Action

• The advantages of the second messenger system, including amplification, regulation, and cross-talk between different systems.

Enzyme Amplification

• Details about how hormone signals increase, or amplify, their effect.

Modulation of Target Cell Sensitivity: Up regulation and Down regulation

• Details about how cells increase (up-regulation) and decrease (down-regulation) receptor activity for hormones.

Target Cell Sensitivity Modulation: Down Regulation

• Mechanisms involved in decreasing receptor activity for hormones.

Hormone Interactions

• Types of interactions between different hormones (additive, permissive, synergistic, antagonistic).

Endocrine Disorders

• Hyposecretion (e.g., inadequate hormone release).
• Hypersecretion (e.g., excessive hormone release).
• Examples of specific disorders relating to the different hormonal glands.

Pituitary Disorders

• Hypersecretion of growth hormone (e.g., acromegaly, gigantism).
• Hyposecretion of growth hormone (e.g., dwarfism).

Thyroid Gland Disorders

• Congenital hypothyroidism, Myxedema, Endemic goiter, Toxic goiter.

Parathyroid Disorders

• Hypoparathyroidism, Hyperparathyroidism

Adrenal Disorders

• Cushing Syndrome, Adrenogenital Syndrome (AGS).

Diabetes Mellitus

• Signs and symptoms of insulin hyposecretion.
• Types of Diabetes Mellitus (Type 1 and Type 2).
• Pathology of Diabetes.

Hyperinsulinism

• Causes and symptoms of hyperinsulinism.

Test your knowledge on different types of cell communication, including direct cell-to-cell interactions and hormones. This quiz will cover various mechanisms such as paracrine, autocrine, and juxtacrine signaling. Understand how these processes impact cellular function and hormone regulation.