endocrine Flashcards
aging and the endocrine system
Ageing negatively affects hormone secretion by the glands of the endocrine system, – older people more prone to insomnia, fractures, diabetes and cognitive changes
Levels of most hormones decrease – such as estrogen (women), testosterone (men), growth hormone, melatonin, aldosterone, calcitonin, renin
Levels of some hormones do not change – such as cortisol, epinephrine, insulin, thyroid hormones T3 and T4
Levels of some hormones increase – such as follicle-stimulating hormone, luteinizing hormone, norepinephrine, parathyroid hormone
Some hormone receptors less receptive – decline in endocrine function
Production rates of some hormones may decrease
Pituitary gland becomes smaller
Thyroid gland becomes more lumpy or nodular; beginning around age 20, metabolism gradually declines
Hormones that usually decrease with age include aldosterone, renin, calcitonin, and growth hormone; specific hormones decrease in older women (estrogen and prolactin) and older men (testosterone).
Hormones that may increase with age include follicle-stimulating hormone (FSH), luteinizing hormone (LH), norepinephrine, and antidiuretic hormone (ADH).
Hormones that remain unchanged or are only slightly decreased with age include thyroid hormones (T3 and T4), cortisol, insulin, epinephrine, parathyroid hormone, and 25-hydroxyvitamin D.
Blood glucose levels rise with age
Insulin levels remain unchanged with age, decreased glucose tolerance may occur due to changes in the cell receptor sites: the older adult experiences hypoglycemia more quickly than a younger person and may progress to dangerously low levels of blood glucose before signs and symptoms are obvious. This decreased glucose tolerance because of cell receptor change can place the older adult at risk for hyperglycemia and the onset of type 2 diabetes.
Thyroid hormone levels may decrease with aging, the body makes up for it by decreasing the rate at which thyroid hormone is broken down; therefore resting levels of thyroid hormone are usually normal in the elderly. Thyroid disorders are, however, twice as common in the older adult. Hypothyroidism is the most common thyroid disorder, especially in older women.
The amount of hormones secreted by the older adult changes, decreasing the individual’s ability to adapt to stress and respond to environmental changes.
principal endocrine glands
Hypothalamus Pituitary Pineal Thyroid Parathyroid Thymus Adrenals Pancreas Ovaries Testes
hormones
Releasing hormones –produced by hypothalamus to trigger the pituitary to release stimulating hormones
Stimulating hormones – stimulate target organs to secrete their hormones
Negative feedback – prevents over-secretion of any hormone; “turns off” the system when the “right point” has been reached
patterns of hormone secretion
Rhythms
Diurnal: day-night/sleep-wake
Prolactin, growth hormone, testosterone secretion during sleep
Circadian: internal process recurring naturally on a 24-hour cycle
Cortisol
Pulsatile, Acute, Cyclic
Pulsatile: secretion of constant level of hormone over a long period
Acute: rapid increase in hormone level for a short time in response to a stimulus
Cyclic: hormone levels increase and decrease in a constant pattern
pathologies of endocrine system hyper states
Hyper-states: increased hormone secretion
Primary disorder: Target gland oversecretes due to pathology directly affecting it
Level of hormone secreted by gland high but the stimulating hormone [from pituitary] level low—due to increased negative feedback from hyperactive target gland secretion
Secondary disorder: Pituitary or hypothalamus over-stimulates a target gland
Target gland hormone and stimulating hormone levels will be high
Ectopic site of hormone production –secretion of hormone by some cancers
Target hormone receptors become hyperactive – genetic mutation
pathologies of the endocrine system hypo states
Hypo-states: decreased hormone secretion
Primary disorder: Target gland undersecretes due to a congenital or acquired problem
Target hormone levels low and stimulating hormone levels high—due to a loss of negative feedback from the hypo-active target gland
Secondary disorder: Pituitary does not secrete enough stimulating hormone
Decrease in target gland hormone and stimulating hormone levels
Tertiary disorder: Hypothalamus does not secrete enough releasing hormone
Defective hormone – high levels of hormone but the function that is supposed to be initiated by the hormone will not occur
Target organ receptor not responsive
High levels of stimulating hormone as the target gland tries to stimulate the target organ to respond
hypothalamus hormones
thyrotropin-releasing hormone (TRH) gonadotropin-releasing hormone somatostatin corticotropin-releasing hormone prolactin-inhibiting factor prolactin-releasing factor
anterior pituitary hormone
adrenocorticotropin hormone (ACTH) thyroid stimulating hormone (TSH) growth hormone prolactin luteinizing hormone (LH) follicle stimulating hormone (FSH)
posterior pituitary hormones
antidiuretic hormone (ADH) oxytocin
alterations of thyroid function
Thyroid hormone (TH) regulates the basal metabolic rate (BMR):
Regulates protein, carbohydrate and fat metabolism
Thyroid secretes two types of hormones:
TH – made up of
Thyroxine (T4) 90% – reservoir for T3
Triiodothyronine (T3) 10% – most active form
Calcitonin –responsive to hypercalcemia
Hyper or Hypo
Hyperthyroidism – hypermetabolism
Hypothyroidism – slowed metabolism
primary thyroid disorders
Pathology of the thyroid gland
Influences levels of thyroid hormone synthesized and secreted
secondary thyroid disorders
Pathology related to the pituitary gland or hypothalamus
Levels of Thyroid- stimulating hormone (TSH) influencing levels of thyroid hormones
risk factors for thyroid disease
Men: age ≥ 60 years
Women: age ≥ 50 years
personal history or strong family history of thyroid disease
diagnosis of other autoimmune diseases
past history of neck irradiation
previous thyroidectomy or radioactive iodine ablation
drug therapies such as lithium and amiodarone
dietary factors (iodine excess and iodine deficiency in patients from developing countries); or
certain chromosomal or genetic disorders (e.g., Turner syndrome,Down syndrome and mitochondrial disease)
hypothyroidism
thyroid hormone deficiency Prevalence 2/100 Canadians Mainly women – middle to older-aged Why? Underactive thyroid function Insufficient amount of thyroid hormone Causes Globally in iodine-deficient regions Iodine deficiency Most common cause in Canada Hashimoto’s thyroiditis
causes of hypothyroidism
Primary Hypothyroidism Hashimoto’s thyroiditis (autoimmune) Congenital Surgical removal of thyroid gland Ablation with radioactive iodine Radiotherapy Thyroid tumour Drug toxicity (lithium, interferon, amiodarone) Secondary Hypothyroidism Disorders of pituitary or hypothalamus
hypothyroidism pathophysiology
Primary: due to thyroid dysfunction
Thyroid hormone level is low and decreases negative feedback on the pituitary: TRH and TSH is high and TH low
related to destruction of thyroid tissue or problems with hormone synthesis
Secondary: due to pituitary dysfunction
Thyroid hormone level is low due to low secretion of TSH by pituitary: TH and TSH low, TRH high
Tertiary: due to hypothalamus dysfunction
Thyroid hormone level is low due to low secretion of TRH by hypothalamus leading to low secretion of TSH by pituitary: TH, TSH, TRH low
Transient: some cases of thyroiditis or on discontinuation of thyroid hormone therapy
clinical manifestations of hypothyroidism
Metabolic: Cold intolerance, modest weight gain hypothermia
Neurologic: Forgetfulness
Psychiatric: Personality changes, depression
Dermatologic: Facial puffiness; sparse, coarse and dry hair; coarse, dry, scaly and thick skin
Ocular: Periorbital swelling, droopy eyelids
Gastrointestinal: Constipation
Gynecologic: Menorrhagia or secondary amenorrhea
Cardiovascular: Slow heart rate
Other manifestations: hoarse voice, and slow speech
hypothyroidism assessment
Observe for early and subtle changes Ask patient about: weight gain and mental changes, fatigue, slowed and slurred speech, cold intolerance, skin dryness, constipation and dyspnea, muscular aches and pains, bradycardia, distended abdomen Patients with hypothyroidism are sensitive to narcotics like opioids (avoid dilaudid, morphine, fentanyl) and other sedatives (could lead to myxedema coma). Recommend use of alternatives for pain such as non-narcotics (Tylenol, Ibuprofen)
complications of hypothyroidism: myxedema coma
Medical Emergency: long history of hypothyroidism with uncontrolled low thyroid production
Precipitated by: illness, infection, trauma, meds that suppress CNS, exposure to cold
Clinical presentation:
Decreased mental status/LOC or coma
Hypoventilation
Hypothermia
Hypotension
Seizures
Shock
Myxedema – thickened, nonpitting edema of skin
hypothyroidism diagnostics/labs
History and physical examination
Serum TSH and free T4 levels
Serum T3 [not sensitive to hypothyroidism] and serum T4 levels
Thyrotropin-releasing hormone (TRH) stimulation test
Thyroid peroxidase (TPO) antibody (TPOAb) test
Thyroid ultrasound – nodules in enlarged gland
Thyroid biopsy – nodules