To an Israelite under the Law of Moses,  kidneys always made them think of sacrifice.  The kidneys and the fat of all animal  sacrifices had to be burnt upon the altar. “Then he  shall offer from the sacrifice of the peace offering,  as an offering made by fire to the Lord, its fat and  the whole fat tail … all the fat that is on the entrails,  the two kidneys and the fat that is on them by the  flanks, and the fatty lobe attached to the liver above  the kidneys … and the priest shall burn them on the  altar as food, an offering made by fire to the Lord”  (Lev 3:9–11 nkjv)

 

kidney

                                                                      Figure . 1 :Iamp’s Kidney’s

The kidneys were offered in the peace offering,  the sin offering and the trespass offering (Lev  3:4,10; 4:9; 7:4). Kidneys also featured in sacrifices for the priests’ sanctification (Exod 29:13,22; Lev  8:16,25; 9:10,19).

Why would the Father especially mark out the kidneys to be offered for so many sacrifices? Why  not the heart or the lungs? The kidneys represent  “the deep seated thoughts of one’s inner self. In  these references where it is so used in Scripture,  it is translated reins (Psa 16:7)” (Martin, 2005,  p.17). The word translated reins and kidney in the  av is the same Hebrew word, kilyah. The kidneys  represent one’s deepest, innermost feelings. When  our innermost thoughts are exercised and directed  by the Word of God, they are of great value to Him.

“Behold, You desire truth in the inward parts,  And in the hidden part You will make me to know  wisdom” (Psa 51:6 nkjv). Also “he is a Jew who  is one inwardly; and circumcision is that of the  heart, in the Spirit not in the letter; whose praise  is not from men but from God” (Rom 2:29 nkjv).

The spiritual significance and symbology of the  kidney is explained in Psalm 26. “The Hebrew word  for reins literally means kidneys. General scriptural  usage indicates that it relates to the innermost  motivation of a man. Whereas the heart (Heb leb) relates to the manifestation of a person’s emotions,  thoughts and inclinations, the ‘reins’ are that part of  a man which decides whether those thoughts and  inclinations will be for good or evil. So the reins can  be tried (Psa 7:9), can instruct (Psa 16:7) and can  act as a person’s conscience (‘I was pricked in my  reins’, Psa 73:21)” (Mellows, 1992, pp.318–319).

The kidneys are the most efficient filters in  existence. As the kidneys filter out that which is bad  and keep that which is good, so a man’s conscience  will cause him to choose the good and reject that  which is bad. This is exemplified in the Lord Jesus  Christ of whom it was prophesied, “Therefore the  Lord Himself will give you a sign: Behold, the  virgin shall conceive and bear a Son, and shall call  his name Immanuel. Curds and honey he shall eat,  that he may know to refuse the evil and choose the  good” (Isa 7:14–15 nkjv).

The kidneys “refuse” or excrete wastes and  toxins while “choosing” to retain useful substances  in the blood.

On a number of occasions we read that the  Father tries both our reins and heart. “I the Lord  search the heart, I try the reins, even to give every  man according to his ways, and according to the  fruit of his doings” (Jer 17:10 kjv).

To please Him, He wants more than just  our emotions or heart. He also wants our inner  deep thoughts and our conscience which directs  and motivates us. “Now the purpose of the  commandment is love from a pure heart, from a  good conscience, and from sincere faith” (1 Tim  1:5 nkjv).

Our kidneys, however, are more than filters of  our blood. The kidneys do not operate in isolation;  they are wonderful organs that interact with many  parts of the body.

The pituitary gland

At the base of the brain lies the body’s master  gland of the endocrine system – the pituitary. This  small gland (about 1 cm in diameter) secretes a  number of hormones that affect how our body  operates. It is unique in that it is the only endocrine  gland that is directly connected to the brain via the  hypothalamus. The pituitary is divided into three  lobes, the anterior, intermediate and posterior.  Each lobe secretes a different set of hormones.  Of particular interest is the hormone released by  the posterior lobe called arginine vasopressin or  antidiuretic hormone (ADH). ADH regulates the  absorption of water by the kidneys.

head

Figure 2: Relationship of kidneys to the “head”

(Images from Astrid Vincent Dinesen)

This is a case of the natural mirroring the  spiritual. Our spiritual head is Christ. “And he put  all things under his feet, and gave him to be head  over all things to the ecclesia, which is his body,  the fullness of him who fills all in all” (Eph 1:22–23  nkjv). “And he is the head of the body, the ecclesia,  who is the beginning, the firstborn from the dead,  that in all things he may have the pre-eminence”  (Col 1:18 nkjv). Our inner man should be directed  by our head, the Lord Jesus Christ.

Water regulation is essential for life. If the  kidneys fail in this role, then without medical  intervention we die. To control and retain water our  kidneys must respond to the hormonal messages  from the head. Water symbolises the Word (Eph  5:26), so for us to live spiritually we must retain  this “water of life” (Rev 21:6).

But some have a seared conscience (1 Tim 4:2)  and cannot retain water and are described as “wells  without water” (2 Pet 2:17), “waterless clouds” and  “twice dead” (Jude 12).

Diabetes

Most of us are aware of the modern diabetes  epidemic. The most common form is diabetes  mellitus where the body either does not produce  enough insulin or does not respond to it. There  is another form called diabetes insipidus. This  disorder causes a person to produce tremendous  quantities of urine. Up to 10 litres or more of urine a  day is typical because the kidneys no longer respond  to ADH. Too little ADH is produced or the kidneys  fail to respond to it.

This is like those who love the water of the Word,  but are unable to retain it. They fail to respond to  their head through a faulty understanding of God,  like those whom Paul describes in 2 Timothy 3:7  (nkjv) as “always learning and never able to come  to the knowledge of the truth.”

Macroscopic structure of the kidney

Each kidney is bean shaped and roughly the size of  one’s fist. Obtain and cut open a kidney; you will  see that it is not uniform in structure. Look carefully  and you will notice that there is some organization.  There are three main areas. The outer more lightly  coloured area is called the cortex; the middle, darker  reddish-brown area, the medulla; and the central  whitish, yellow funnel like area, the renal pelvis.  These areas are more clearly shown by the artist in  the following illustration.

brian

                                                                                Figure  3: Parts of the kidney

The blood supply

Both kidneys are only about 0.5% of total body  weight. While quite small they receive a huge  amount of blood, 20% of that pumped by the  heart. This blood is filtered by the kidneys at a rate  of about 125mL/minute. Over a 24 hour day this  amounts to a staggering 180 litres. As the volume  of blood in one’s body is 7–8 litres, the entire blood  supply is filtered 20 to 30 times every day.

The nephron

nephron

                                                                Figure 4: A nephron (not of scale)

The kidneys are mentioned once in the New  Testament. “And I will kill her children with death;  and all the ecclesias shall know that I am he which  searcheth the reins and hearts: and I will give unto  every one of you according to your works” (Rev  2:23 kjv).

The Greek word for reins (kidney) is nephros.  From this word we get nephrosis, the term for  kidney disease, and nephron, the functional unit  of the kidney. Every kidney has one to two million  nephrons. A simplified nephron is depicted in  Figure 4.

Every nephron starts with a structure called the  glomerulus.

The spherical structure is called Bowman’s  capsule and it houses a network of capillaries (the smallest blood vessels) known as the glomerulus  capillaries. Combined these are called the renal  corpuscle. The glomerulus is situated in the kidney’s  cortex.

Blood enters the glomerulus through an arteriole, and blood pressure in the glomerulus  forces water and dissolved substances and small  protein molecules from the blood into Bowman’s  capsule. This is called ‘filtrate’ and the kidneys  generate about 40 litres of filtrate a day.

The glomerular filtrate flows along the first part of the renal tubule called the proximal convoluted  tubule, then into the loop of Henle and finally  along the distal convoluted tubule. The tubule wall  is incredibly thin – just one cell thick – and has  a large number of transport proteins within this  wall. These transport proteins latch on to various  small molecules in the filtrate as it flows past and  moves them into the cell. Each transport protein is  specific to one or two molecules. Sometimes useful  molecules are passively transported back into the  blood while others require energy. The kidneys are  the second most active body tissue after exercising  muscles. These amazing tiny tubules work very hard  to maintain your blood chemistry!

Kidney tubule

In this first section of the nephron – the twisted  proximal convoluted tubule – water, glucose,  vitamins, amino acids, and minerals (sodium, potassium bicarbonate and chloride) are reabsorbed  from the filtrate into the blood.

Next, the loop of Henle, is a narrow section of  the nephron tubule that has a descending limb, a tight hair-pin bend and an ascending limb. From the  diagram of the nephron one might think this loop is  quite short. However the diagram is not to scale – it  would be impossible to draw a scale diagram and  still see the various structures. The loop is 2–3cm  long, descending all the way from the kidney cortex  down into the medulla and back to the cortex.

The reabsorption of water from the collecting  tubules is controlled by the pituitary gland through  the production of ADH. The absorption of water  from the collecting tubules only occurs when ADH  is present. The more ADH present the more water  is absorbed.

The posterior lobe of the pituitary has special  nerve cells that sense the concentration of salts  in the blood. If the concentration is high, ADH  is secreted and more water is absorbed. If the  concentration is low, less ADH is excreted and  less water is absorbed. The concentration of salts is  directly related to the amount of water in the blood.  The saltier the blood, the more water is reabsorbed  by the kidneys and the more concentrated one’s  urine becomes. As we drink more, the reverse  happens and the volume of urine increases as the  excess water is excreted.

The kidneys are very small organs but they  are essential for survival and a healthy life. They  work long and hard excreting toxic wastes and  maintaining a constant internal environment by  keeping the blood’s concentration within strict  limits.

Kidney hormones and enzymes

The kidneys work in harmony with many other parts  of the body to regulate:

  • blood pressure via the production of the enzyme Renin
  • calcium levels through the conversion of cholecalciferol into Vitamin D, and
  • the manufacture of red blood cells by the secretion of erythropoietin (which is used by elite athletes to increase their red cell count).

The best medical technology cannot replicate all  these functions of the kidney, like controlling blood  pressure and the kidney’s rapid response to changes  in our blood chemistry. People with kidney failure  are helped by renal dialysis but the only cure for  kidney failure is a kidney transplant. Only the organ  Yahweh designed can do the whole job. We truly  are wonderfully made. How could such an intricate organ with all its highly specialised anatomy and  functions have come about by chance! How are the  “wise (taken) in their own craftiness” (1 Cor 3:19).

In 1 Corinthians 12:20–31, Paul deals with  the body and demonstrates that all our parts are  important. No organ can operate independently  of others and even those we rarely consider (“less  honourable”) are vitally important. The kidneys  fit this category; you don’t think about them until  something goes wrong! They extract and excrete daily body wastes because these wastes are like  “the sin which doth so easily beset us”. Wastes are  the product of things we do. These intricate little  organs that work constantly to keep us clean within  are like the Word of God and the forgiveness that  makes us spiritually clean. Kidneys are essential  to the health of the whole body and they work in  concert with other bodily organs.

Paul adds in verse 26, “And if one member  suffers, all the members suffer with it; or if one  member is honoured, all the members rejoice with  it”(nkjv). So, if our kidneys suffer and fail, all the  other members of the body are affected, even to  the point of death. We are all members of the one  body of Christ. “Now you are the body of Christ,  and members individually” (1 Cor 12:27 nkjv). We  must all be considerate of one another and not fall  into the mistake of presuming some to be less or  more worthy than others.

Martin, J. (2005). The Schoolmaster. CSSS.

Mellows, R. (1992). Psalms, An Introduction to the  Psalter (1–41). CSSS.