Human Nutrition And Digestion

Requirements of a Balanced Human Diet

Discuss about the Human Nutrition and Digestion.

1. There are seven requirements for a balanced human diet which include water, proteins, carbohydrates, fats, vitamins, minerals and fibre or roughage (Rolfes, Pinna& Whitney, 2015). There are various types of food sources under these diverse classes of balanced diet requirement. The primary purpose of advocating for balanced diet among individuals is in order to achieve and sustain good health. Although all these requirements are necessary for daily diet, there are guidelines for consumption which determine the ratios and amount of intake according to recommended dietary allowances (RDA). Water is vital for the humans, and it makes up averagely about 70% of the body weight. Water requirements and recommended consumption of water per day depend on various factors which include physical activities undertaken, age and environmental conditions. Therefore there are natural and automatic mechanisms through which the body regulates the need for water consumption by controlling thirst centers within the brain. Much of the water in the body is within the intracellular spaces while some are within the extracellular spaces, majorly the cardiovascular system as blood (Katz, Friedman & Lucan, 2015). The primary roles of water, especially in the cardiovascular system, is to aid transportation of other nutrients such carbohydrate products, amino acids, minerals and vitamins to all body parts and their cells, assisting in getting rid of harmful toxins from the body through sweating and through the urinary system and it moistens certain membranes in the body such as nose, lungs, ears among several others. The most common sources of water are fluid foods, fruits, direct intake of water through drinks and foods with moisture content in them.

Protein is another requirement to meet the balanced diet. The roles of this macronutrient in the body are to repair and maintain body tissues. They are essential in the healing process of wounds. Additionally, they are the ones utilised by the body to make enzymes and hormones that control different physiological functions. Proteins also are the ones that make a significant part of antibodies that provide body immunity. Furthermore, they are involved in the transportation of protein-bound molecules throughout the body besides controlling the plasma oncotic pressure. Moreover, it is a source of energy in the absence of enough energy production from carbohydrates. Proteins can be derived from animal based food such as fish, animal meat, eggs and milk products. From plants, they can be derived from leguminous plant seeds such as beans and lentils (Elia, & Nutrition Society (Great Britain), 2013).

Sources and Roles of Water

Carbohydrates have several functions in the body. Firstly, they are the primary source of energy. Consequently, they spare the use of proteins for energy hence preventing ketosis that is associated with utilization of proteins for energy. They are also a source of glycogen that makes part of body cells that are made up of glycoproteins. Food sources of this macronutrient are cereals such as maize, millet, sorghum and rice, beverages, fruits and legumes.

Fats in a similar way play the role of energy source in the body in some instances such as when one is starving. They also aid in the absorption, transportation and distribution of some essential nutrients such as vitamin A, D, E, K and drugs in the body that are lipid soluble. Fats make the adipose tissue that provides insulation and guarding against loss of heat hence maintaining body temperatures within normal ranges besides providing cushion and acting as shock absorbers around vital organs. Fats can be obtained from food sources such as fish, animal meat, milk, cheese and chicken. They are also available in some plants such as grains, seeds, and nuts. They can equally be obtained from cooking oils and fats (Grodner, Escott-Stump & Dorner, 2016).

Vitamins are classified into water and fat or lipid soluble. Fat soluble vitamins are A, D, E and K.  The rest such as vitamin B complexes and C are water soluble. Their sources are also different. However, there are some that share a common source. The following is a simplified table showing the origin and roles of these vitamins in the body according to Walter, Hornig, Moser, & European Academy of Nutritional Sciences, 2013.

Vitamin	Source	Function
A	Egg yolk, liver, dark leafy vegetables, fortified milk products	Maintenance of healthy mucous membranes, bones, and prevention of night blindness
B complex	Avocado, meat, eggs, brown rice, milk	Red blood cell production and sustenance of the nervous system
C (ascorbic acid)	Fruits such as lemons and oranges	Promotes wound healing, absorption of iron and it acts as an antioxidant
D	Fish, fortified milk products	Helps in absorption of calcium
K	Cabbage, meat, cereals, liver, dark leafy vegetables	Helps in blood coagulation

Mineral such as sodium, potassium, iodine, iron, chlorides and calcium are required by the body and therefore are needed in daily diet in recommended amounts. These minerals can be obtained from food sources such as liver, kidney, eggs, fish, iodized salt, beans, milk, vegetables, cereals, and nuts. They are meant for different purposes in the body including blood pressure regulation by potassium and sodium, normal heart functioning by potassium and calcium, haemoglobin formation by iron, production of thyroid hormones by iodine, bone formation and maintenance by calcium and phosphorus besides calcium also playing a role in blood clotting.

Fibre or roughage’s primary function is ensuring normal functioning of the digestive system. It increases motility of the gastrointestinal system besides providing the bulk needed in movement and elimination of intestinal contents. The primary source of roughage is foods high in cellulose such as vegetables and fruits; cabbage, spinach, kales, mangoes, oranges and lemon. Roughage is neither digested nor absorbed in the digestive system of humans.

Sources and Roles of Proteins

2. The purpose of calculating the body mass index (BMI) is usually to determine the health of an individual by knowing the amount of fat in the body based on their height and weight. BMI is essential in the diagnosis of obesity which is a risk factor for diseases such as diabetes type 2 and cardiovascular diseases (Ferrera, 2013). On the other hand, it can determine malnutrition hence prompting nutritional interventions on an individual. It is determined by getting a quotient through the division of a person’s weight in kilograms and the square of their height in meters. The normal BMI ranges are 18.5-25.0 kg/m². This technique is, however, unreliable in some instances such as when used in children since it is meant to be used in adults only. Its validity can also be affected if one is pregnant, has severe extremity oedema, ascites or has somebody deformities affect the accuracy of an individual’s BMI. In such instances, other means of determining body fat are used such as waist and middle upper arm circumferences (Vermeulen & De, 2012).

BMI calculation examples:

BMI of a male adult with a height of 1.7 metres and 80 kilograms

BMI is 80÷1.7^{2 =}27.68 kg/m² (the individual is overweight)

BMI of a female adult with a height of 1.62 meters and 50 kilograms

BMI is 50÷1.62²=19.05 kg/m² (within normal BMI ranges)

BMI of a female child 14 years old with a height of 1.3 meters and a weight of 29.1kgs

BMI=29.1÷1.3² =17.2 kg/m^2, then determine the percentile they belong while considering age in the BMI chart. In this case, the child is in the 5^th percentile and therefore deemed underweight.

3. (a) Nutritional deficiency is a lack of adequate amount of a particular nutrient in the body hence resulting in a certain nutritional disorder. Nutritional deficiency may be either due to lack of enough intake of that particular nutrient or due to malabsorption. On the other hand, imbalanced diet is the intake in either excess or less than the recommended dietary amounts per day of particular nutrients. Deficiency of iron is causes iron deficiency anaemia that is characterised by brittle nails, weakness, and fatigue, pallor on the skin, dizziness and shortness of breath. Protein deficiency causes kwashiorkor that has characteristic symptoms which include muscle weakness; muscle cramping stunted growth reduced muscle mass and ascites. Vitamin K deficiency typically causes coagulopathies in which blood clotting may occur slowly or not occur depending on the extent of the deficiency, leading to massive There is a number of causes of imbalanced nutrition such as poverty, lack of access all nutrient food sources, lack of nutritional education and certain eating disorders (Wardlaw & Byrd-Bredbenner, 2013).

Sources and Roles of Carbohydrates

(b)

Type of amino acid	Examples
Essential amino acids are those that cannot be naturally produced by the body and therefore are required to be obtained from food consumed	Phenylalanine, leucine, lysine, valine, methionine, threonine, tryptophan, histidine and isoleucine.
Non-essential amino acids are the ones that are produced by the body and are not necessary needed to be part of the diet.	alanine, arginine, glutamic acid, and glycine

4. Javid and Alicia being male and female respectively aged 27 years have different dietary needs which they should meet by intake of various nutrients according to recommended dietary allowance (RDA) thus preventing nutritionally related diseases. The RDA for male his age recommends a total of averagely 2550 kcal per day while that for her age is 2000kcal per day (Shils & Shike, 2016). This energy should be obtained from various nutrients as follows:

Nutrient	Proteins	Fats	Carbohydrates	Fibre	Cholesterol	Vit A	Vit C	Ca	Na
Javid (male)	68g	71g	351g	26g	300mcg	750mcg	30mcg	0.4-0.5g	0.4-0.5g
Alicia (female)	58g	56g	275g	20g	300mcg	750mcg	30mcg	0.4-0.5g	0.4-0.5g

5. The labelled parts of the digestive system are:

The mandibular salivary gland which is an irregular sac-like structure on the floor of the mouth whose function is to secrete saliva into the mouth cavity (Tamir, 2012).

The gall bladder is a small sac-like structure beneath the liver whose function is collection and storage of bile produced by the hepatic cells of the liver.

Bile duct is a tubular structure that connects and conveys bile from the gall bladder to the duodenum

The liver is a smooth glandular organ with lobes in the abdominal cavity whose function is detoxification, regulation of body temperature and secretion of bile.

The duodenum is the first part of the small intestines after the stomach into which secretion of bile and pancreatic juice occur to aid in the digestion of fats and other nutrients.

Appendix is a finger-like structure in the ileocecal junction which is vestigial and functionless. However, it has lymphoid cells and hence may have immunological functions.

The oesophagus is a tubular structure that connects the mouth and the stomach whose function is to allow movement of ingested substances from the mouth to the stomach.

The diaphragm is a dome-shaped structure separating the abdominal and thoracic cavities. Its role is aiding in breathing and defecation (Walker, 2015).

The stomach is a sac-like structure between the oesophagus and the duodenum in the digestive system. Its primary function is secretion of hydrochloric acid for digestion and churning of food to form chyme in the process of mechanical and chemical digestion.

Pancreas, a feather-like structure is both an endocrine and exocrine gland that secretes pancreatic juice with enzymes for digestion of food, insulin and glucagon hormones for regulation of glucose in the blood (Netter, 2014).

The descending colon is a tubular structure whose function is the absorption of water and electrolytes besides allowing faecal matter to descent towards the sigmoid colon.

Sources and Roles of Fats

The jejunum is a highly coiled middle part of the small intestines in which much of absorption of almost all nutrients occurs (Enger, Ross & Bailey, 2012).

The rectum is a sac-like structure after the sigmoid colon and before the anus which provides storage for the faecal matter before elimination through defecation.

The anus is an opening at the end of the digestive system. It is composed of the anal sphincter, and its function is to allow removal of faecal matter through defecation (Barrett & Ganong, 2012).

6. istologically, the stomach consists of a simple columnar epithelium. It has surface mucous cells that secrete mucin to the epithelial lining. Its lining has gastric pits and gastric glands on their bases. Its muscularis is also composed of oblique, circular and longitudinal layers from inside outwards. The duodenum has tall villi and crypts in it and Brunner’s glands. Its epithelium is lined by cuboidal epithelium. On the other hand, the ilium is composed of tiny finger-like projections called villi and microvilli. Its lining is covered by simple columnar cells. These villi contain venules and arterioles for blood supply and transportation of absorbed food. Both the duodenum and the ileum have four layers namely the mucosal layer that has lamina propria and muscularis mucosa lined with simple columnar epithelium (lamina epithelialis) that has enterocytes as well as goblet cells for mucus production, submucosa, muscularis propria and the serosa. (Lowe, Anderson & Stevens, 2015).

Fig 1.0: Histological structures of the stomach

Fig 1.1: Histological structures of the ileum

(a) (i) Intracellular digestion is the breakdown of particles of substances within the cells with the aid of enzymes such as hydrolytic enzyme released by lysosomes.

(ii) Extracellular digestion is a breakdown of food substances into smaller particles outside the body cells such as within cavities such as the buccal cavity and the stomach.

(iii) Mechanical digestion is the physical breakdown through chewing and other means of ingested substances into smaller particles (Wingerd, 2014).

(iv) Chemical digestion is the breakdown of ingested food into simpler building blocks of a nutrient with the help of chemicals such as enzymes and hydrochloric acid.

(b) The ham sandwich of bread, butter and ham has three major nutrients which are carbohydrates, fats, and proteins. With bread, starch, in the mouth, it is partially broken down by salivary amylase to form maltose. In the duodenum, the remaining sugars are acted upon by pancreatic amylase to form more maltose. In the small intestines, maltase enzyme further breaks down maltose into glucose molecules. Further, sucrose and lactase digest sucrose and lactose respectively into glucose and fructose, galactose and glucose in that order. These end molecules are readily absorbed into the bloodstream in the small intestines (McArdle, Katch & Katch, 2014). Fats in butter are acted on by salivary and gastric lipases to hydrolyze them to glycerol and fatty acids. In the small intestines, bile salts secreted from the gall bladder aid in further emulsification. The pancreatic lipase, cholesterol ester hydrolase, and phospholipase chemically break down the fats and lead to end resultant substances: monoglycerides, fatty acids, cholesterol, lysolecithin, and glycerol. These elements are made soluble by mixing with micelles after which they are delivered to the intestinal epithelial cells brush-border membrane and diffuse into the cells and into the bloodstream via the lymphatic system. Ham, protein is digested in the stomach and duodenum where it is enzymatically broken down by pepsin-trypsin and chymotrypsin into dipeptides and eventually into amino acids which are absorbable in the small intestines (Lipski, 2012).

Lacteals are part of the lymphatic system in the villi. Their primary function is to provide absorption mechanisms of molecules that are too large to pass and be transported in the bloodstream through capillaries in the villi. Similarly, these capillaries play a role in the transportation of absorbed small sized nutrients such as glucose, mineral salts, and vitamins through the bloodstream (Davenport, 2015).

Fig 1.2: Lacteal and blood capillaries in the villus

References

Barrett, K & Ganong, W 2012, Ganong’s review of medical physiology, McGraw-Hill Education LLC, New York.

Davenport, H 2015, Physiology of the digestive tract: An introductory text, Year Book Medical Publishers, Chicago.

Enger, E, Ross, F & Bailey, D 2012, Concepts in biology, McGraw-Hill, New York.

Elia, M & Nutrition Society (Great Britain) 2013, Clinical nutrition, West Sussex:Wiley Blackwell, Chichester.

Ferrera, L 2013, Focus on body mass index and health research, Nova Science Publishers, New York.

Grodner, M, Escott-Stump, S & Dorner, S 2016, Nutritional foundations and clinical applications: A nursing approach, Elsevier Mosby, St. Louis, Missouri.

Katz, D, Friedman, R & Lucan, S 2015, Nutrition in clinical practice: A comprehensive, evidence-based manual for the practitioner, Wolters Kluwer, Philadelphia.

Lipski, E 2012, Digestive wellness: Strengthen the immune system and prevent disease through healthy digestion, McGraw-Hill, New York.

Lowe, J, Anderson, P & Stevens, A 2015, Stevens & Lowe’s human histology, Elsevier/Mosby, Philadelphia.

McArdle, W, Katch, F & Katch, V 2014, Exercise physiology: Energy, nutrition, and human performance, Lippincott Williams & Wilkins, Philadelphia.

Netter, F 2014, Atlas of human anatomy, Saunders/Elsevier, Philadelphia.

Rolfes, S, Pinna, K & Whitney, E 2015, Understanding Normal and Clinical Nutrition, Cengage Learning, Stamford.

Shils, M & Shike, M 2016, Modern nutrition in health and disease, Lippincott Williams & Wilkins, Philadelphia.

Tamir, E 2012, The human body made simple, Churchill Livingstone, Edinburgh.

 Walker, R 2015, Human body, DK Publishers, New York.

Vermeulen, A & De, S 2012, New trends in body mass index research, Nova Biomedical/Nova Science Publishers, New York:

Walter, P, Hornig, D, Moser, U & European Academy of Nutritional Sciences 2013, Functions of vitamins beyond recommended dietary allowances, Karger, Basel.

Wardlaw, G & Byrd-Bredbenner, C 2013, Wardlaw’s perspectives in nutrition, McGraw-Hill Higher Education, New York.

Wingerd, B 2014, The human body: Concepts of anatomy and physiology, Wolters Kluwer/Lippincott Williams & Wilkins, Philadelphia.