W7 The endocrine system

Endocrine system

Collection of ductless glands that produce hormones and deliver to blood stream/lymph/tissue fluid

Glands - Pineal, pituitary, thyroid, parathyroid, adrenal, ovaries, pancreas and testes

Hormone action

• Control internal environment by regulating chemical composition and blood volume

• Respond to changes in environmental conditions, help body cope with infection/trauma/stress/dehydration

• Assist with growth and development

• Contribute to reproduction

• Help regulate metabolism and energy balance

Hormones produced from tissue within other organs

Gastrin, Secretin and Erythropoietin (EPO)

Exocrine glands

Excrete product via duct to environment external to itself, either inside body (i.e. pancreatic juices into digestive tract) or on surface of body (i.e. sweat onto skin)

Endocrine glands

Secrete products (hormones) directly into blood, lymph or tissue fluid, without requirement for duct (ductless glands)

Hormone travel

Chemicals that travel through bloodstream until reach target organ, exert effect

Autocrine hormones

Effect on original cell that produced it

Paracrine hormones

Effect on local cells/tissues

Homeostasis

Regulates internal environment to maintain stable condition e.g. pH or temperature

Synthesis

Creation/production of substance, e.g. hormone

Metabolic rate

Amount of energy expended during normal cellular processes

Pituitary Gland

Ventral to forebrain, divided into anterior and posterior lobe.

Posterior lobe physically connected to hypothalamus

Responds to releasing hormones secreted by hypothalamus, by producing stimulating hormones

Thyroid and parathyroid glands

Thyroid glands either side of upper part of trachea, caudal to/level of larynx. Thyroid gland secrete 3 hormones (metabolism and calcium regulation)

2 parathyroid glands associated with each lobe of thyroid, secrete 1 hormone (calcium regulation)

Pancreas

Mixed gland - endocrine and exocrine functions

Secretes pancreatic juice to aid digestion (exocrine)

Hormones (endocrine)

Situated behind stomach, secretes 3 hormones in regulation of glucose

Adrenal glands

Glands on top of kidneys

Consist medulla, cortex covered by connective tissue capsule

Cortex and medulla considered 2 different endocrine glands

Medulla - fight/flight hormones

Cortex - steriod hormones

Ovaries

2 ovaries, one either side of midline dorsal peritoneal cavity

3 hormones

Testes

2 testicles, descending into scrotum

2 hormones

Hormones can be

• Proteins - growth hormone, insulin, adrenocorticotrophic hormone (ACTH)

• Peptides - thyroid-stimulating hormone (TSH), oxytocin

• Amines - dopamine, adrenaline

• Steroids - cortisol, progesterone

Endocrine system relies on

negative feedback to ensure correct hormone and amount released

based on homeostasis

Hormone production/inhibition

Based on feedback loop, conditions within internal environment stimulate hormone release or prevent production

e.g. hormone balance to maintain glucose/calcium levels in blood

Negative feedback loop

Endocrine gland interpret information in blood to determine hormone to stop production

Thyroid and parathyroid glands regulation

Regulate blood calcium levels

• High levels - parathryoid hormone release inhibited (increases calcium)

• Low levels - calcitonin release inhibited (decreased calcium levels)

Negative feedback

Positive feedback loops

Parallel to negative system, stimulating hormone production (or activating target cell) in response to blood levels

Reverse negative feedback

• Levels high, calcitonin released to lower blood calcium levels

• Levels low, parathyroid hormone released to increase blood calcium levels

Positive feedback systems

Also stimulate action in target cell

Brain Glands

Pineal, hypothalamus and pituitary

Pineal gland

pea-sized organ, centre of brain

produces melatonin (basis for serotonin)

Pineal photoperiod

Sensitive to levels of light essential for functioning of reproduction, behaviour and coat changes

Associated with seasonal affective disorder (SAD), sleeping dysfunction and stimulating reproductive calling in cats

Hypothalamus

Control centre of endocrine system

Produces 7 hormones:

• Prolactin releasing hormone (PRH)

• Dopamine

• Growth Hormone Releasing hormone (GHRH)

• Somatostatin

• Thyrotropin releasing hormone (TRH)

• Gonadotropin Releasing hormone (GRH)

• Corticotropin releasing hormone (CRH)

Prolactin releasing hormone (PRH)

Stimulates release of next messenger (prolactin) from anterior pituitary gland

Dopamine

Wide influences on activity, inhibits release of prolactin via negative feedback

Growth Hormone releasing hormone (GHRH)

Stimulates release of next messenger (GH) from anterior pituitary gland

Somatostatin

Inhibits release of GH via negative feedback

Thyrotropin releasing hormone (TRH)

Stimulates release of next messenger (TSH) from anterior pituitary gland

Gonadotropin releasing hormone (GRH)

Stimulates release of next messengers (FSH, LH fem, FSH ICSH male) from anterior pituitary gland

Corticotropin releasing hormone (CRH)

Stimulates release of next messenger (ACTH) from anterior pituitary gland

Pituitary gland

Infleuences production of pituitarys hormones

Pituitary gland stimulation

Stimulated by releasing hormones secreted by hypothalamus, produces appropriate stimulating hormones within pituitary

Released into blood to reach target organs

Anterior pituitary (adenohypophysis)

Hormones released from hypothalamus primarily act upon anterior pituitary, creating cascade of messages which circulate to stimulate distal glands/tissues

Anterior lobe responsibility

Production/release of hormones that regulate bodily acitivities,

Hormones in anterior pituitary, FATLIPS

Follicle-stimulating hormone (FSH), Adrenocorticotrophic hormone (ACTH), Thyroid-stimulating hormone (TSH), LH/ICSH, prolactin and somatotropin/GH

Adrenocorticotrophic hormone (ACTH)

Targets cortex of adrenal glands, stimulating production of corticosteriods (cortisol)

Thyroid-stimulating hormone (TSH)

TSH stimulates thyroid gland to release thyroxine - T3 (inacitve form); T4 (active form)

Posterior pituitary gland (neurophypophysis)

Posterior pituitary regulates itself (no input from hypothalamus)

Produces - oxytocin and ADH/vasopressin

Antidiuretic hormone (ADH) / Vasopressin

Released due to increased osmotic pressure within blood.

ADH targets collecting ducts to increase permeability, causing increase in reabsorption of water, increasing plasma volume, reducing urine produced

Reproductive glands ovaries & testes

Follicle-stimulating hormone (FSH) and luteinising hormone (LH) are gonadotropins secreted by anterior pituitary gland

Ovaries

Oestrogen, progesterone and relaxin

Testes

Testosterone & Oestrogen