Endocrine System Flashcards
1
Q
Name some of the key endocrine glands of the body?
A
Pituitary, thyroid, parathyroid, hypothalamus, adrenal glands, pancreas
2
Q
At what speed do hormones effect the body?
A
Slow - chronic effect
3
Q
What are the two classifications of hormones?
A
Steroids and non-steroids
4
Q
What are the 3 types of non-steroid hormones?
A
Amino acid derivatives
Peptides
Glycoproteins
5
Q
Steroid hormones are based on the ring structure of which basic organic chemical molecule?
A
Cholesterol
6
Q
Name 5 examples of steroid hormones?
A
Cortisol
Aldosterone
Testosterone
Oestrogen
Progesterone
7
Q
What are the two types of amino acid derivative (Non-steroid) hormones?
A
Amines and Iodinated amino acids
8
Q
What are some common amine type amino acid derivatives of non-steroid hormones?
A
Adrenaline (epinephrine)
Noradrenaline (norepinephrine)
Melatonin
9
Q
What are some common iodinated amino acids type amino acid derivatives of non-steroid hormones?
A
Triiodothyronine
Tetraiodothyronine (thyroxine)
10
Q
What are the two types of non-steroid, peptide hormones?
A
Long chain (proteins) and short chain peptides
11
Q
What are some examples of short chain non-steroid peptides?
A
Antidiuretic hormone
Oxytocin
Melanocyte stimulating hormone
Somatostatin
Thyrotropin releasing hormone
Gonadotropin releasing hormone
Atrial natriuretic hormone
12
Q
What are some examples of long chain (proteins) non-steroid peptides?
A
Growth hormone
Prolactin
Parathyroid hormone
Calcitonin
Adrenocorticotropic hormone
Insulin
Glucagon
GI tract hormones (secretin, CCK, gastrin)
13
Q
Many peptide hormones are produced in a precursor form, i.e pre-hormone —> prohormone, where does this take place?
A
In the endoplasmic reticulum
14
Q
What are prohormones?
A
An inactive precursor of a hormone
15
Q
When does a prohormone become activated?
A
When it is packaged in Golgi apparatus (modified) . It is secreted from the cell via vesicles
16
Q
Follicle Stimulating hormone and Luteinizing hormone (both involved in female menstruation cycle) are what type of non-steroid hormones?
A
Glycoprotein
17
Q
What are some hormone-like substances which have a paracrine effect?
A
Prostagrandins
Leucotrienes
Thromboxane
18
Q
What are the functions of local tissue hormones?
A
Blood flow regulation
Haemostasis
Mucosal protection (stomach)
Inflammation
19
Q
What type of endocrine effect do local tissue hormones typically exert?
A
Paracrine
20
Q
What are two common second messengers in the effect of non-steroid hormones?
A
cAMP and Ca++
21
Q
Where are hormones mainly metabolised?
A
In the liver
22
Q
Which type of hormones can travel through the cell membrane?
A
Steroid hormones because they are hydrophobic
23
Q
What term describes over-secretion and under-secretion of hormones?
A
Hypersecretion and hyposecretion
24
Q
What might further complicate hyposecretion and hypersecretion?
A
The number of receptors present.
25
What is downregulation?
Loss of receptors overtime
26
Having more hormone receptors is known as?
Upregulation
27
Having more hormone receptors is known as?
Downregulation
28
What mechanism typically regulates hormone secretion?
Negative feedback mechanisms
29
What is Hyperfunction?
Hypersecretion + Upregulation
Failure to metabolise hormone
30
What is Hypofunction?
Hyposecretion + Downregulation
Receptors non functioning
31
What are the function of Hypothalamus?
1- Thermoregulation
Negative feedback loop
2- Hormone secretion
Primary and trophic hormones
3- Circadian rhythms
Day/Night cycle
4- Motivation
Thirst , feeding, sexual behaviour
5- Emotions
32
What are the two pituitary glands?
Anterior & Posterior
33
What are the two types of hormones released from the hypothalamus?
Primary and Trophic hormones
34
Thirst, feeding and sexual behaviour are all do to motivation caused by which endocrine gland?
Hypothalamus
35
What is the role of the hypothalamus in relation to the circadian rhythm?
By responding to day/night cycles
36
Where do releasing hormones from hypothalamus go?
To AP via blood vessels {Hypothalamic-pituitary portal vessels} ,that will trigger release of hormones from AP.
37
Name the blood vessels that used to carry releasing hormones from the hypothalamus to AP?
Hypothalamic-pituitary portal vessels
38
How do hormones travel from hypothalamus to posterior pituitary compared to anterior pituitary?
Via nerve axons in Posterior and blood vessels in anterior
39
What are some hypothalmic hormones?
-Corticotropin releasing hormone (CRH)
-Gonadotrophin releasing hormone (GRH)
-Thyrotropin releasing hormone (TRH)
-Growth hormone releasing hormone (GHRH)
-Somatostatin (SS) (GH inhibiting hormone)
-Prolactin releasing hormone (PLRH)
-Dopamine (DA) (also PLIH)
40
Name some Anterior Pituitary hormones?
-Adrenocorticotropic hormone (ACTH)
-Follicle stimulating hormone (FSH)
-Luteinising hormone (LH)
-Thyroid stimulating hormone (TSH)
-Growth hormone (GH)
-Prolactin (PL)
41
What hormone stimulates cortisol release from adrenal cortex?
ACTH\ adrenocorticotropic hormone
42
Detail the corticotrophins pathway leading to cortisol secretion?
The hypothalamus secretes corticotrophin-releasing hormone (CRH) which stimulates the anterior pituitary gland to secrete adrenocorticotrophic hormone (ACTH). ACTH travels via the bloodstream and stimulate the secretion of cortisol from the adrenal glands.
43
Detail the Gonadotrophins hormone pathway?
Nerve cells (neurons) in your brain's hypothalamus gland make and release GnRH into your blood vessels. The hormone then travels to your pituitary gland at the base of your brain. GnRH stimulates your pituitary gland to make and release follicle-stimulating hormone and luteinizing hormone.
44
What effect does FSH have on the ovaries and testes?
Ovaries - Ovum maturation/ Oestrogen production
Testes - Sperm production
45
What effect does LH have on the ovaries and testes?
Ovaries - Production of oestrogen & Progesterone
Testes - Testosterone production
46
Detail the thyrotrophin hormone pathway?
47
Detail the Somatotrophins hormone pathway
48
Detail the Prolactin hormone pathway?
49
Name the hormones released by the Posterior pituitary gland
ADH
Oxytocin
(Produced in Hypothalamus)
50
Name the two nuclei that produce Oxytoxin and ADH
The paraventricular nuclei produce the hormone oxytocin, whereas the supraoptic nuclei produce ADH.
51
What is the action/function of ADH
Produced in Hypothalamus, Released by Posterior pituitary
Function: Increases Water reabsorption in DCT and collecting ducts via promoting aquaporin insertion
52
Name the Stimuli for Oxytocin release?
Stretch of Uterus
Infant suckling
53
Name the function of Oxytocin once released from the Posterior Pituitary?
Contraction o Uterus & Milk Ejection
54
Where is Calcitonin produced?
par-follicular (C-cells) in Thyroid gland
55
What are some thyroid hormones?
T3: tri-iodo-thyronine
T4: tetra-iodo-thyronine (‘thyroxine’)
Calcitonin (regulates calcium levels)
56
What are the functions of Thyroid Hormones?
- Determine basal metabolic rate
- Increase metabolic rate of cells
- Normal foetal and childhood growth
- Involved in upregulating adrenoreceptors
57
What is the clinical significance of hypothyroidism (adult life mainly)?
Cretinism, Myxoedema
58
What is the clinical significance of hyperthyroidism (child life mainly)
Graves disease- Exophathalmos
59
What name is given to the bump associated with thyroid swelling due to iodine deficiency?
Simple Goitre
60
What hormone dose parathyroid gland produce?
PTH → Increases serum calcium via activating osteoclast activity
61
What 3 hormones does the Pancreas produce?
Insulin
Glucagon
Somatostatin
62
Where are Islets of Langerhans lying?
In the exocrine tissue
63
What are some functions of Insulin?
Key function: Lowers blood glucose
Facilitates Glucose uptake into muscle cells & Adipocytes
Also involved in Formation of :
- Glycogen
- Triglycerides
- Facilitates protein synthesis
64
How does Insulin lower blood glucose?
Facilitates glucose entry into:
- Muscle cells, adipocytes
Promotes formation of:
- Glycogen
- Triglycerides
- Facilitates protein synthesis
65
What are some activities which promote insulin secretion?
- Increased Blood glucose
- Increased blood amino acids
- Glucose dependant, insulinotropic peptide
- Vagus Nerve activity
66
What are some activities which inhibit insulin secretion?
- Adrenaline
- Sympathetic Nerve
- Somatostatin
67
Mention the functions of glucagon
Acts to raise blood glucose via:
- Glycogenolysis in liver
- Gluconeogenesis in liver
- Lipolysis and Ketone synthesis
68
How does Glucagon raise blood glucose?
Promotes:
- Glycogenolysis in liver - breakdown of glycogen
- Gluconeogenesis in liver - formation of glucose
- Lipolysis and ketone synthesis
69
What are some activities which promote glucagon secretion?
Decreased blood glucose
Increased blood amino acids
Cholecystokinin
Autonomic nerve activity
70
What are some activities which inhibit glucagon secretion?
insulin
somatostatin
71
What are some clinical features of Diabetes mellitus?
Polyuria (increase urine production)
Polydipsia (increase fluid intake; thirst)
Glycosuria (glucose in urine)
Diabetic neuropathy
Skin and oral diseases, incl. periodontitis, xerostomia
72
Which type of diabetes results in destruction of beta cells in the Pancreas?
Type 1 Diabetes
73
How is Type 1 Diabetes managed?
Diet control & Insulin Injections
74
What is Type 2 diabetes characterised by?
Insulin independent - Decreased sensitivity of target cells to insulin
75
How is Type 2 Diabetes managed?
Diet, oral hypoglycaemic agents
76
What term is used to describe the adrenal gland position on the kidneys?
Supra-renal
77
What are some cortex hormones released form cortex of adrenal glands
- aldosterone
- cortisol
- androgens
78
What cells of the adrenal cortex produce cortisol?
Zone fasciculata cells
79
Cortisol controlled by what hormone?
Adrenocorticotropic hormone (ACTH) from AP
80
What are the actions of cortisol?
Metabolic effects, permissive effects (Adrenaline), Anti-inflammatory and immunosuppressive role
81
What cells of the adrenal cortex produced aldosterone?
Zona glomerulosa
82
What system controls aldosterone release?
RAAS
83
What are the actions of Aldosterone?
-Promotes reabsorption of Na and H20 in the kidney DCT
- Increase exertion of H,K
84
What cells of the adrenal cortex produced androgens?
Zona fasciculata & Reticularis
85
What are the functions of Androgens?
Growth + Sexual characteristics - Pubertal growth
86
Excess glucocorticoid - Cortisol secretion can cause what condition?
Cushing’s syndrome
87
Excess androgen secretion can cause what condition?
Adreno-genital syndrome
88
What are the two parts of adrenal gland?
Cortex and Medulla
89
What hormones are released from medulla of adrenal glands?
adrenaline and noradrenaline
90
Which types of nerves control the adrenal medulla?
Sympathetic
91
Adrenal insufficiency cause?
Addison’s disease - low levels of Cortisol and aldosterone
92
How our body gains water?
- Ingestion - Food/drink
- Formed via metabolism
93
How our body losses water?
- Excretion - Urine/Faeces
- Evaporation - Sweat, Air
94
What is GFR?
Glomerular filtration rate (120 ml/min)
95
What is NFP?
Net filtration pressure (10-15mmHg)
96
Where most of the obligatory reabsorption occurs?
Proximal convoluted tubule 60 – 70%
97
What part of the nephron responsible for concentration of urine?
Loop of Henle
98
What Hormones control the activities that occurs in the distal convoluted tubule?
Aldosterone
Atrial natriuretic hormone
ADH (in most distal parts)
Parathyroid hormone
99
What are the activities that occur in the distal convoluted tubule?
Reabsorption of water, Na+, Cl–, Ca2+
Secretion of H+, K+
100
What are the other names of Atrial Natriuretic Hormone (ANH)?
ANF, ANP
101
Where does ADH produced and released?
Antidiuretic hormone is produced in hypothalamus and released from posterior pituitary gland
102
What is vasopressin?
Antidiuretic hormone (ADH)
Acts on distal convoluted tubules (distal end) and collecting ducts to increase water permeability
By insertion of aquaporin channels, water moves passively along osmotic gradient between tubule lumen and interstitial fluid.
103
What are the two different ways to release ADH?
104
Na+ regulations
105
Na+ regulations
106
K+ regulation
K+ is an important electrolyte in membrane potential establishment
- Small changes can have big effects on nerve/muscle function
- Regulated by Aldosterone (Same as Na+)
107
Effects of K+ on nerve function
- Increased K+ ECF → Increased depolarisation
- Membrane potentials do not/struggle to return to ‘rest’
- Axon remain in prolonged ‘refractory period’
108
How K+ used in toothpastes to reduced sensitivity?
109
Disorders of ADH secretion
- Hypo-secretion
- Diabetes insipidus
- Hyper-secretion
- Syndrome of Inappropriate ADH (SIADH)
- Excess water retention
110
What is shock?
The decreased in blood volume that result in a fall in blood pressure and impaired delivery of nutrients.
111
What are the physiological responses to blood loss?
- Immediate - Stop the bleeding
- Short term - Restore blood pressure
- Medium term - Restore fluid volume
- Long term - Replace blood constituent
112
Explain vascular response in immediate response
- Spasm due to trauma - Myogenic dilation & Humoral vasoconstriction
- Endothelium - Platelet adhesion/aggregation
- Endothelium - Facilitate anticlotting & fibrinolysis (Haemostasis)
113
Explain platelet response in immediate response
Turbulent flow via vessel damage causes platelet contact with vessel wall
- Platelets adhere & clump together
- Chemical release enhances aggregation
- Forms platelet plug
114
Where most of the clotting factors are made?
Liver
115
What vitamin requires to presence in synthesis of clotting factors?
Vitamin K
116
What happen in plasma response?
- Coagulation cascade
Cascade responsible for the conversion of fibrinogen → Fibrin - Forms a stable blood clot
117
Which pathway is important in initiating clotting after an injury?
Extrinsic pathway
118
What is Fibrinolysis?
Dissolves fibrin clot once it has served purpose,this is undertaken by an enzyme plasmin
119
Which baroreceptors detect the reduction of blood pressure?
Arterial baroreceptors
120
Explain baroreceptor reflexes that happens in short term response
Mediated by - Sympathetic nerves
Hormones involved:
- Adrenaline
- Angiotensin II
- Vasopressin (ADH)
121
How Blood Volume is restored via Increasing interstitial fluid reabsorption?
Arteriole vasoconstriction → Decreased capillary BP
Decreases hydrostatic pressure force
More fluid reabsorbed/retained due to oncotic pressure
122
How Blood Volume is restored via decreasing fluid loss in kidney?
- Reduced GFR decreases solute concentration in DCT
- Na+ change detected by Juxta-medullary apparatus
- RAAS activated → ADH, Aldosterone, Vasoconstriction, Thirst
123
How Blood Volume is restored via Increasing fluid intake?
Hypothalamic mediated desire to drink
Stimuli:
- ⬆️ Plasma Osmolarity
- ⬇️ ECF volume
- Angiotensin II
- Dry mouth
124
What is Erythropoiesis?
Process of making red blood cells (erythrocytes)
125
Explain erythropoietin secretion
126
Shock types
- Hypovolaemic shock
⬇️ ECF volume - due to haemorrhage, sweating, diarrhoea, burns
- Low resistance (or disruptive) shock
⬇️ Peripheral resistance - due to widespread vasodilation e.g. anaphylactic shock
- Cardiogenic shock
Heart failure to acts as a pump
127
What is shock?
Acute loss in blood pressure, inadequate blood flow to tissues
128
What is stress?
A force applied to a body causing deformation or strain
129
Examples of some Stressors
130
What are the systems that involve in complex interaction of stress?
- Nervous ⚡
- Endocrine 🧪
- Immune 🦠
131
Mention Stages in Stress?
Stages in Stress - General Adaption Syndrome
1- Alarm Reaction ⏰
- Fight, Flight, Fright responses
- Physiological effects
2- Resistance phase
- Adapting to Stressor
3- Exhaustion phase 😮💨
- Sever, persistent Stress
- If response is futile (weak) → system fails
- Various pathological effects
132
What are the components of alarm response stage?
- Neural - Sympathetic nervous system
- Hormonal - Adrenaline & Corticosteroids
133
Sympathetic fibers run from where to where?
T1-L2 of spinal cord
134
What are the effects of sympathetic innervation?
- ⬆️ CO (HR & Contractility)
- 🩸 Redistribution of CO
- Increased flow to muscle,
-Decreased flow to GIT, Kidney e.c.t
- ⚛️ Metabolic
- Glycogenolysis (Glycogen → Glucose)
- Adipose metabolism
- 🧪 Stimulation of adrenaline release
135
What are the effect of Adrenaline in 1st stage of stress?
Secreted from - Adrenal Medulla
Function: Augments & Prolongs action of SN
Increased SN function upregulates:
- Increase CO
- Redistribution of blood flow
- Metabolic effects
136
Glucocorticoids - Cortisol
Secreted from - Adrenal Cortex
Functions:
- ⬆️ energy production from glucose, amino acids & Fats
- ⬆️ permissiveness of adrenaline (Enhances effects)
- Anti-inflammatory actions
- Immunosuppression
137
What are anti-inflammatory actions of Cortisol?
- Inhibit prostaglandins & Leukotrienes
- Inhibit helper T cells
- ⬆️incidence of illness during stress
138
What is corticosteroids therapy?
-Act as anti-inflammatory drugs (E.g. Arthritis)
-Long term therapy can disrupt homeostatic control - CRH & ACTH
-Increases risk during dental procedures
139
What is the main stress hormone?
Cortisol
140
What is Stress Analgesia?
Diminishment of pain sensation induced by stress
141
What causes analgesia during stress?
- Release of endogenous opioid peptides
- Release of endorphins
- Release of enkephalins - opiates
142
What might make the patient stress?
sounds - smells - equipment - treatment severity- LA- pain
Dental phobic patients - May present with higher levels of anxiety
143
What might make dentist stress?
Standing
Complex/difficult procedures
Anxious patients
Supervising a student’s first extraction
144
What happens in resistance phase?
Adaption Phase - Coping with Stress
Persistent exposure to stressor(s) → Causes response to diminish (adaptation)
Individual has gained resistance
145
In the exhausting phase, what happens if there is a failure to overcome/adapt to stressors?
That is will lead to:
- Adrenal failure
- Immunosuppression
- Peptic Ulcers
- CVS disease
- Death - In extreme cases 💀
146
What are the functions of Calcium?
Form bone and tooth structure
Mineral store
Action potentials (cardiac muscle) Membrane excitability
Acts as a 2nd messenger
- Muscle: excitation-contraction coupling
- Gland secretion
- Non-steroid hormone action
Co-factor in metabolic pathways
Blood clotting
147
What are the hormones and minerals involved in Calcium homeostasis?
PTH
Calcitonin
Vitamin D
148
How PTH acts to increase plasma calcium?
- Osteoclast stimulation - Increased bone resorption
- ⬆️ Ca2+ resorption in kidney (Paired with increased PO4 excretion)
- ⬆️ Uptake of Ca2+ from intestine (assisted by vitamin D)
149
How calcitonin act to lower plasma calcium?
- Osteoblast stimulation - Increased formation of bone
- ⬇️ Ca2+ resorption in kidney
150
What are the sources of Vitamin D?
Dietary & 7-dehydrocholesterol synthesis
151
What hormones increased bone formation?
Calcitonin
Growth hormone
IGF-1
Insulin
Oestrogen
Testosterone
152
What hormone increase bone resorption?
Cortisol
PTH
Thyroid hormones
153
Osteoblasts
Synthesise and secrete collagen fibres forming a matrix later mineralised by calcium salts
154
Osteocytes
Trapped osteoblasts in the bone matrix
155
What is the process that osteocyte use when contact with other cells?
Long cytoplasmic processes
156
From which cells do osteoclast derived from?
Macrophages
157
What is the name of the cavity that osteoclast lie in?
Howship’s Lacunae
158
What are the reasons of Hypocalcaemia?
Hypo → Low calcium in blood
- Due to: Decreased Ca intake, Excessive Ca loss, Alkalosis
- Results in: ⬆️ Nerve excitability (Pins & Needles, spasms)
159
How Alkalosis an arise?
From Hyperventilation due to rapid expiration of CO2 (Altering pH balance of blood).
Trapping CO2 → via rebreathing expired air from a bag can help settle symptoms
160
What is Hyperparathyroidism?
Over secretion/activity of PTH → Hypercalcaemia
Causes: Osteitis fibrosa cystica → Demineralisation in skull and leg bones
161
What is Hypoparathyroidism?
Low activity of PTH → Hypocalcaemia
Causes: Defective mineralisation (Can affect teeth development/integrity)
162
What are the causes of Vitamin D deficiency?
- Stemming from dietary deficiency
- Synthesis failure
- ⬇️ GIT uptake
163
What Vitamin D deficiency can lead to?
- Undermineralised bone (Soft and flexible)
- Children → Rickets
- Adults → Osteomalacia
164
What is Osteoporosis?
bone disease
Decreased bone mass/density
Loss of Matrix → Secondary loss of mineral
Common in elderly (evident earlier in women)
Other causes: Corticosteroids, Nutritional deficiency
165
What is Osteopetrosis?
Increased bone mass/density
Causes restricted/reduced blood supply
Prone to fracture and chronic infection
Dental related → difficult extractions
166
What we call an increase in cell numbers?
Hyperplasia
167
What we call an increase in cell size?
Hypertrophy
168
Give examples of cells that can regenerate and others cannot
Can regenerate: Liver, skin, blood cells
Cannot: neurons
169
Growth is affected by?
-Genes, heredity
-Environment: Nutrition-Disease-Growth factors, e.g. hormones
170
What Hormones that influencing growth?
Thyroid hormones
Growth hormone
Sex hormones
Others :Insulin, Cortisol, Vitamin D, PTH
171
How thyroid hormone can affect growth?
Indirectly affect growth - important for normal growth & development
Facilitates action of growth hormone and sympathetic NS
E.g. Protein synthesis in brain of foetus & infant
E.g. Development of neuron
172
What is Hypothyroidism ?
When Thyroid gland does not produce enough hormones.
Clinical features/symptoms: Sparse hair, Large tongue, mental impairment
Deficiency impedes brain 🧠 and skeletal 🦴 growth - Delayed tooth eruption 🦷
173
What is the treatment of hypothyroidism?
Treatment: Thyroxine supplements → may see improvement in mental function. Recovery may not be complete
174
What is the function of the GH?
Possesses metabolic and growth-promoting actions
Main effects during: postnatal period, infancy & adolescence
175
How Metabolic actions of growth hormone mostly indirect?
⬆️ Blood glucose levels - acts as ‘anti-insulin’
⬇️ Decreased glucose uptake by cells
⬆️ Lipolysis - fatty acids readily available for energy production
⬆️ Facilitates amino acid uptake - for protein synthesis
176
How IGF-1 (Insulin-like growth factor) affect growth?
Produced in liver
- Exerts growth effects alongside GH
- Responsible for cartilage, bone, soft tissue and viscera development
177
What are the effects of sex hormone in growth?
Effects:
- Bone growth stimulation
- Accelerate epiphyseal growth plate closure - end of bones
- Testosterone - anabolic effect on protein synthesis - ⬆️ Muscle bulk (Form of anabolic steroid)
178
Insulin & Growth
No direct effects on growth
Contributions of insulin:
- Promotes foetal growth
- Promotes post-natal growth via IGF-1 secretion stimulation
- Facilitates protein synthesis by making glucose readily available
179
Cortisol & Growth
Elevated levels → Inhibit growth
Actions of cortisol:
- Stimulates protein catabolism (Breakdown)
- Supresses bone growth and bone resorption
Elevated levels contribute to growth-retarding effects
180
Vitamin D,PTH & growth
Contribute to growth via ensuring calcium and phosphate availability for bone formation (Bone homeostasis)
- Vitamin D → Ca2+ absorption in gut
- PTH raises plasma Ca2+ levels
181
What we call the accelerates normal growth in childhood?
Gigantism
182
What we call appositional growth occurs in extremities → Hands, feet, jaw ⬆️ in bulk?
Acromegaly
183
What is Achondroplasia?
Defective cartilage growth
Characterised by: Short arms & Thighs
Attributed to: Genetic mutation of Growth hormone receptor gene
184
What is ageing?
Involves the gradual deterioration of all parts of the body → Reduced body system performance
Can be complicated by disease
185
Life span depends on what ?
- Genetics
- Environment
- Nutrition
- Lifestyle
- Disease absence
186
Why apoptosis occurs?
-In development; e.g. tooth germ, nervous system
-To replace ‘worn out’ cells
-To destroy tumour cells
