Autonomic and Endocrine Systems: Key Concepts and Blood Cell Types

Autonomic Nervous System (ANS)

Division of the nervous system that helps regulate activity of major organ systems and is not under conscious control.

Central nervous system (CNS)

Brain and spinal cord.

Peripheral nervous system (PNS)

Nerves outside the brain and spinal cord.

Visceral reflexes

Reflexes involving internal organs.

Baroreflex

ANS visceral reflex that responds to blood pressure changes detected by arterial stretch receptors.

Baroreceptors

Arterial stretch receptors that detect high blood pressure.

Medulla oblongata

Brainstem region that integrates information and makes decisions in the baroreflex.

Vagus nerve (CN X)

Carries efferent signals to the heart in the baroreflex, slowing the heart and lowering blood pressure.

Negative feedback loop

A feedback system that responds to change by moving the value back toward the optimal range.

Sympathetic division

Fight-or-flight division of the ANS that prepares the body for physical activity.

Fight-or-flight

Sympathetic response that increases heart rate, blood pressure, airflow, and blood sugar.

Parasympathetic division

Rest-and-digest division of the ANS that calms body functions and conserves energy.

Rest-and-digest

Parasympathetic response that supports digestion, waste elimination, and normal maintenance.

Autonomic output pathway

ANS pathway in which a signal travels across two neurons to reach an organ.

Preganglionic neuron

First autonomic motor neuron; cell body is in brainstem or spinal cord and axon extends to an autonomic ganglion.

Autonomic ganglion

Site where the preganglionic neuron synapses with the postganglionic neuron.

Postganglionic neuron

Second autonomic motor neuron; cell body is in an autonomic ganglion and axon extends to the target organ.

Acetylcholine (ACh)

Neurotransmitter secreted by all preganglionic neurons in both ANS divisions.

Norepinephrine (NE)

Neurotransmitter secreted by nearly all sympathetic postganglionic neurons.

Sympathetic NS

ANS division that diverts blood to skeletal muscles, mobilizes glucose, increases respiration, heart rate, and alertness.

Widespread sympathetic effects

A single preganglionic fiber can synapse with 10+ postganglionic neurons and affect multiple organs.

Adrenal gland

Paired gland on top of the kidneys with cortex and medulla.

Adrenal medulla

Inner region of adrenal gland with chromaffin cells that release epinephrine and norepinephrine into blood.

Chromaffin cells

Modified postganglionic neurons in the adrenal medulla stimulated by preganglionic neurons.

Epinephrine

Hormone released mainly by adrenal medulla; increases heart rate, blood pressure, airway dilation, blood glucose, and blood flow to muscles.

Parasympathetic NS

ANS division that diverts blood to digestive and urinary systems, conserves energy, and reduces respiration and heart rate.

Selective parasympathetic effects

Preganglionic neurons terminate in or near target organs and stimulate only one or a few organs.

Target cell receptor

Protein that determines how a target cell responds to the same neurotransmitter or hormone.

Cholinergic neuron

Neuron that secretes acetylcholine.

Cholinergic receptor

Receptor that binds acetylcholine.

Muscarinic receptors

ACh receptors found on cardiac muscle, smooth muscle, and glands; act through second messenger cascades.

Nicotinic receptors

ACh receptors on postganglionic neuron cell bodies in autonomic ganglia, adrenal medulla cells, and NMJs; always excitatory.

Adrenergic fibers

Fibers that release norepinephrine.

Adrenergic receptors

Receptors that respond to norepinephrine or epinephrine.

Alpha-adrenergic receptors

Usually excitatory receptors for norepinephrine/epinephrine that use second messengers.

Beta-adrenergic receptors

Usually inhibitory receptors for norepinephrine/epinephrine that act through cAMP as a second messenger.

Endocrine system

Glands and tissues that secrete hormones and stimulate changes in other tissues or organs.

Hormones

Chemical messengers secreted into blood that act on target cells.

Target cells

Cells with receptors that allow them to respond to a hormone.

Neuroendocrine relationship

Nervous and endocrine systems overlap because some hormones are secreted by neurons and some neurotransmitters act as hormones.

Glycogenolysis

Conversion of glycogen to glucose.

Pituitary gland (hypophysis)

Endocrine gland formed of adenohypophysis and neurohypophysis.

Adenohypophysis

Anterior pituitary; cuboidal epithelium that produces six major hormones.

Neurohypophysis

Posterior pituitary; nervous tissue linked to hypothalamus that secretes OT and ADH transferred to it.

Infundibulum

Stalk that suspends the pituitary gland.

Sella turcica

Bony depression where the pituitary gland sits.

Hypothalamo-hypophyseal tract

Nervous tract linking the hypothalamus to the posterior pituitary.

Oxytocin (OT)

Posterior pituitary hormone involved in uterine contractions, milk ejection, and bonding.

Antidiuretic hormone (ADH / vasopressin)

Posterior pituitary hormone that increases water retention in kidneys and raises blood pressure.

Hypophyseal portal system

Blood vessel system that carries hypothalamic hormones to the anterior pituitary.

Thyroid-stimulating hormone (TSH)

Anterior pituitary hormone that stimulates release of thyroid hormone.

Luteinizing hormone (LH)

Anterior pituitary hormone that stimulates release of ovarian and testicular hormones.

Follicle-stimulating hormone (FSH)

Anterior pituitary hormone that stimulates follicular growth in ovaries and sperm production in testes.

Adrenocorticotropic hormone (ACTH)

Anterior pituitary hormone that stimulates release of adrenal glucocorticoids.

Hypothalamus

Brain region that secretes releasing/inhibiting hormones and produces OT and ADH for the neurohypophysis.

Endocrine axis

Relationship between hypothalamus, pituitary, and a third endocrine gland.

Hypothalamic/cerebral control

Brain control of pituitary secretion based on monitored body conditions.

Neuroendocrine reflexes

Reflexes controlling posterior pituitary secretion, such as ADH release from osmoreceptors or oxytocin from suckling.

Osmoreceptors

Hypothalamic receptors that detect changes in blood osmolarity and trigger ADH release.

Positive feedback

Feedback in which a change causes more change in the same direction until a specific endpoint.

Prolactin

Anterior pituitary hormone that stimulates milk production in mammary glands.

Prolactin-inhibiting hormone (PIH)

Hypothalamic hormone that decreases prolactin release.

Growth hormone (GH / somatotropin)

Anterior pituitary hormone with widespread effects because most organs have GH receptors.

Mitosis

Cell division; stimulated by growth hormone for body growth.

Cellular differentiation

Process of cells becoming specialized; stimulated by growth hormone during growth.

Growth hormone-releasing hormone (GHRH)

Hypothalamic hormone that stimulates GH release.

Somatostatin

Hypothalamic/pancreatic hormone that blocks GH release and regulates glucagon and insulin.

IGF-I

Growth-stimulating factor produced by liver that prolongs the action of GH.

Protein synthesis

Effect of GH that boosts transcription and translation and suppresses protein catabolism.

Carbohydrate metabolism

GH effect that mobilizes fatty acids and reduces dependence of cells on glucose.

Electrolyte balance

GH effect that promotes Na+, K+, and Cl- retention and enhances Ca2+ absorption.

Thyroid gland

Largest endocrine gland; secretes thyroid hormone and calcitonin.

Thyroid hormone (TH)

Hormone made by follicular cells and stored in colloid; includes T3 and T4.

Follicular cells

Thyroid cells that produce thyroid hormone.

Colloid

Material inside thyroid follicles where thyroid hormone is deposited/stored.

Thyroxine (T4)

Tetraiodothyronine; iodine-based thyroid hormone.

Triiodothyronine (T3)

Iodine-based thyroid hormone.

Functions of thyroid hormone

Increases metabolic rate and heat production; raises oxygen use, heart rate, breathing rate, alertness, and reflex speed.

Thyrotropin-releasing hormone (TRH)

Hypothalamic hormone that stimulates the anterior pituitary to release TSH.

Endemic goiter

Thyroid swelling due to excess TSH, often from iodine deficiency.

Iodine deficiency

Lack of iodine that prevents enough thyroid hormone production and can cause goiter.

Calcitonin

Hormone from thyroid parafollicular cells that lowers blood calcium.

Parafollicular cells (C cells)

Thyroid cells that produce calcitonin.

Osteoclast inhibition

Calcitonin effect that decreases bone breakdown.

Osteoblast stimulation

Calcitonin effect that promotes bone formation.

Parathyroid glands

Four small ovoid glands on posterior side of thyroid gland.

Parathyroid hormone (PTH)

Hormone that raises blood calcium by promoting bone resorption and kidney calcium reabsorption.

Pancreas

Organ with both exocrine and endocrine functions; endocrine hormones come from pancreatic islets.

Pancreatic islets (islets of Langerhans)

Endocrine cell clusters in pancreas important in blood glucose regulation.

Glycemia

Blood glucose concentration.

Alpha cells

Pancreatic islet cells that secrete glucagon when blood glucose falls.

Glucagon

Hormone that raises blood glucose by stimulating gluconeogenesis, glycogenolysis, and glucose release.

Gluconeogenesis

Formation of glucose from fats or amino acids.

Beta cells

Pancreatic islet cells that secrete insulin when blood glucose rises.

Insulin

Hormone that helps cells store or metabolize blood glucose and blood fats; prevents breakdown of fat or protein.

Delta cells

Pancreatic islet cells that secrete somatostatin.

Paracrine regulator

Hormone regulator that acts locally on nearby cells.

Pancreatic polypeptide (PP)

Hormone secreted by PP cells after a meal; reduces pancreatic enzyme secretion.

Pineal gland

Endocrine gland that produces melatonin at night and helps maintain circadian rhythms.

Melatonin

Pineal hormone produced at night and linked to circadian rhythms.