Summary IB biology SL - Option D: Human physiology
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Course
IB Biology SL
Institution
Gymnasium Am Münsterplatz
Book
Pearson Baccalaureate Biology Standard Level 2nd Edition Print and Ebook Bundle for the IB Diploma
Complete summaries and study guides on the chapters of Pearson Baccalaureate's Biology Standard Level IB book. Detailed summaries of up to 10 pages with illustrations. These documents helped me get a good 6 in the IB exams of May 2019 :)
--> This document is on Option D: Human physiology
Essential nutrients:
A nutrient is a chemical substance found in foods and used in human boy. Essential nutrients cannot be
synthesized from other molecules by the human body and must thus be part of our diet.
- Essential minerals:
Inorganic substances with specific roles in making anatomical structures (calcium in bones) or a
physiological role incorporated into important molecules (iron within haemoglobin). → long-lived
molecules = small need for minerals.
→ Calcium: repair of bones I body, always recycled but some of it is lost
→ Iron: synthesis of RBC in liver, always recycled but some of it is lost
→ electrolytes (charged): involved in synaptic transmissions, muscle contractions e.g. Ca 2+, Na+, Mg2+
- Vitamins:
Organic substances, synthesised by living organisms but some organisms also rely on an intake of vitamins
from others, small intake → long-lived substances
→ Vitamin C: most animals apart from humans synthesise Vitamin C, gene code for one of the enzymes
involved in the synthesis of vitamin C from glucose is defective in all humans; important for immune
system, bones, teeth etc. → deficiency = scurvy
→ Vitamin D: formation of bones; can be synthesized by skin’s epidermis when stimulated by ultraviolet
rays of sun (often not sufficient and risky) → deficiency = rickets (in children) or osteomalacia
(deformities in bones)
- Fatty acids:
Two fatty acids are required in our diet because we lack the enzymes to make these fatty acids from other
fatty acids. = omega-3 and omega-6
- Amino acids:
Nine of the 20 amino acids are essential (others are only essential for some people). The human body has
no storage mechanisms for amino acids, so AA must be part of our regular diet; one has to make sure to
eat a variety of AA sources. → people who are dependent on a single staple of e.g. corn (deficient in two
essential amino acids) can suffer from deficiency symptoms
Phenylketonuria (PKU)
Genetically inherited disease caused by a persons’ inability to metabolize the AA phenylalanine. This
inability is a result of a autosomal recessive allele that codes for the production of the enzyme
phenylalanine hydroxylase. As this enzyme is not present, the phenylalanine builds up in tissues and the
bloodstream = mental deficiencies, behavioural problems, seizures etc.
→ no cure but treatment: diet limited in protein sources high in phenylalanine
Eating and nutrition disorders
- Appetite is controlled by the hypothalamus
Appetite and satiety mechanisms seem to be a combination of feedback loops from the nervous system,
the digestive system and the hormonal system.
→ After a meal, the pancreas releases hormones reducing appetite.
→ During a meal, your stomach expands and stimulates cells of the vagus nerve which then sends signals
to the hypothalamus to stop eating.
→ The intestines produce hormones to send signals about hunger and satiety to the hypothalamus.
→ cells of adipose tissue produce hormone leptin sending a message to hypothalamus to suppress
appetite
= People with conditions damaging their hypothalamus can have appetite problems
Consequences of being overweight
- Hypertension
One of the factors causing hypertension is weight as, the more you weigh, the more blood you need to
supply oxygen and nutrients to cells → volume of blood increases = pressure on walls of arteries
- Type II diabetes
, Body cell resistance to the effect of insulin and a decrease in insulin production → correlated but why?
Nutrition problems and their consequences:
- Deficiencies
Apart from vitamin deficiencies, there also exist deficiencies from essential substances such as calories:
When there is a lack of calories, the body will first draw upon glycogen storages, then body fat and lastly
protein. When energy is not available from any of these three, the body starts digesting body tissues e.g.
skeletal muscle for energy. → muscle gets thinner
- Imbalance
In parts of the world where people rely on a limited variety of foods, there can be a nutrient imbalance.
→ e.g. too many carbohydrates, specific deficiency for essential nutrients
- Excess of nutrients = obesity
Abnormal fat accumulation can have serious consequences for a human’s health. Culprits: change in types
and quantities of food people eat, change in amount of physical activity
D.2 Digestion
Exocrine secretions:
Exocrine secretions are produced by exocrine glands and are taken to specific locations by a duct.
→ surface of body: tears secreted from lacrimal glands + perspiration produced by sweat glands + milk
→ lumen of alimentary canal: variety of digestive exocrine secretions needed in specific parts
Exocrine secretion Exocrine gland Ducts leading to Function of secretion
Saliva Salivary glands Mouth Moistens food +
enzyme amylase
Gastric juice Three cell types in pits Interior of stomach Mucus protecting
of stomach wall stomach, hydrochloric
acid (HCl) denatures
proteins + enzyme
pepsin
Pancreatic juice Pancreatic cells Duodenum Trypsin, lipase and
amylase + bicarbonate
solution neutralizes
partially digested food
entering from stomach
Bile Liver Gall bladder and Emulsification of lipids
duodenum
Gastric secretions:
There are three types of glandular cells called gastric
pits on the inner lining of the stomach.
- Before eating, your stomach is being
prepared for digestion (thought, taste, smell
of food) → autonomic nervous system sends
impulses to medulla oblongata of brainstem
- Medulla responds using the parasympathetic
division of the ANS.
- Action potentials are sent by vagus nerve to
the stomach
- Gastric pits begin HCl and pepsinogen
production and secretion
→ when pepsinogen meets HCl, it is transformed into its protein digesting enzyme = pepsin
- Same action potentials stimulate gastric pits to secrete gastrin hormone
- Gastrin enters the blood and is carried to other stomach cells = further stimulates secretion of
HCl and pepsinogen = positive feedback
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